Chapter I: Part 1

TRANSCRIBER’S NOTE

Italic text is denoted by _underscores_.

Footnote anchors are denoted by [number], and the footnotes have been placed at the end of the chapter.

A superscript is denoted by ^x or ^{xx}, for example und^r or 36^{th}.

Corrigenda on page xiv have been applied to the etext except for illustration corrections.

Illustrations without captions have had a description added.

Some minor changes to the text are noted at the end of the book.

INVENTIONS

OF THE

ANCIENTS

HERO OF ALEXANDRIA
]

THE

PNEUMATICS

OF

HERO OF ALEXANDRIA

FROM THE ORIGINAL GREEK

TRANSLATED FOR AND EDITED BY

BENNET WOODCROFT

PROFESSOR OF MACHINERY IN UNIVERSITY

COLLEGE LONDON

LONDON
TAYLOR WALTON AND MABERLY
UPPER GOWER STREET AND IVY LANE PATERNOSTER ROW
1851

TO

HIS ROYAL HIGHNESS PRINCE ALBERT

PRESIDENT OF THE SOCIETY OF ARTS

This Work

IS BY SPECIAL PERMISSION MOST RESPECTFULLY

DEDICATED

BY HIS ROYAL HIGHNESS’S OBEDIENT AND

VERY HUMBLE SERVANT,

BENNET WOODCROFT.

EDITOR’S PREFACE.

While the Editor of the present work was engaged in writing an _Analytical History of the Steam-Engine_, it became necessary to consult the antient mechanicians to ascertain who were the inventors of the several parts composing that machine: the earliest writer on the subject appeared to be Hero of Alexandria; throughout whose work so many of the elementary parts of all Steam-Engines, and those also of most other machines are mentioned, that it was thought a translation of Hero’s Pneumatics would be acceptable not only to the Engineer but to the scientific world generally.

Although at the commencement of his work, Hero states that he has added his own discoveries to those “handed down by former writers,” yet in no instance has he pointed out any thing which originated with himself; nor is there any statement in the text, except the one I have just quoted, which would lead the reader to any other conclusion than that the whole is a compilation from the works of those who at that period of time were styled the “antient philosophers and mechanicians.”

Those parts of each vessel or instrument which mechanically perform the operations assigned to them are alike, or nearly so, in the four manuscript and the three printed copies of Hero’s works which have been consulted by the Editor; but great diversity of form is given to the vessel in which they are placed. The drawings have been made expressly for this work from the best examples.

The seventy-eighth proposition is the only instance in which there is an omission of the illustrative drawing, and this occurs in all the copies; the two drawings which are now supplied to that proposition have been made from the descriptions given in the text.

For the Translation of Hero from the Greek, the valuable assistance of Mr. J. G. Greenwood, Fellow of University College, London, has been obtained: he is the recently appointed Professor of the Languages and Literature of Greece and Rome, in Owen’s College, Manchester.

It is confidently hoped that this Translation will be found superior to its predecessors in whatever language; and that it will prove not only generally interesting but practically useful.

TRANSLATOR’S PREFACE.

Concerning Hero of Alexandria, the author of the treatise here translated, little is known with certainty. When his name and the place of his abode have been given, all that can be positively affirmed is exhausted. We are further told by Hero the younger, who is supposed to have written in the seventh century A. D., that Hero, the author of the “Pneumatics,” was a pupil of Ctesibius;—a statement sufficiently probable from the character of his works, and strengthened by the inscription Ἥρωνος Κτησιβίου[1] prefixed to another work by Hero on the construction of missiles.

Even the precise period at which Hero lived is a debated point. From his own writings all that can be gathered is that he knew the works of Archimedes, and of Philo the Byzantian, who, again, is known to have been a contemporary of Ctesibius; and, as the earliest mention of him by others is as low down as the fourth century A. D., external evidence, even if it were distinct, would be little trustworthy. Such evidence, however, is vague and scanty. The only direct statement bearing on the date of Hero is the assertion that he was the pupil of Ctesibius. The date of Hero therefore depends on the date of Ctesibius, and this has been variously fixed by different chronologists.

Clinton, (F. H. vol. iii. pp. 535, 538,) who puts Hero as low down as the end of the second century B. C., proceeds on the following evidence: Athenæus (vol. iv. p. 174, edit. Schweighæuser) quotes one Aristocles as saying, in a work περὶ χορῶν, of the water-organ, φασὶ τοῦτο εὑρῆσθαι ὑπὸ Κτησιβίου κουρέως ἐνταῦθα οἰκοῦντος ἐν τῇ Ἀσπενδίᾳ ἐπὶ τοῦ δευτέρου Εὐεργέτου· διαπρέψαι τέ φασι μεγάλως. Now Euergetes II. (Ptolemy VII.) reigned from B. C. 170 to B. C. 117, and hence Clinton assigns Hero, the pupil of Ctesibius, to the reign of Ptolemy VIII. that is, to B. C. 117–81.

Fabricius, on the other hand, (Bibi. Græc. vol. iv. pp. 222, 234, edit. Harl.) setting out from an entirely different datum, places him more than a hundred years earlier, in the time of Ptolemy Philadelphus (Euergetes I.): Athenæus Mechanicus, (one of the mechanical writers whose works are printed in the _Veterum Mathematicorum Opera_), in his treatise περὶ μηχανημάτων, p. 8, speaks of Ctesibius as a contemporary; his words are Κτησίβιος ὁ Ἀσκληνὸς, ὁ ἐν Ἀλεξανδρείᾳ μηχανικός. This treatise is dedicated to a Marcellus, and Fabricius, assuming, after Hero junior, this Marcellus to be the conqueror of Syracuse, has hence assigned Ctesibius and Hero to the reigns of the second and third Ptolemies (B. C. 285–222).

Of these conflicting dates that assigned by Clinton has been generally adopted. The question is discussed at some length by Schweighæuser, in a note on the passage of Athenæus referred to above: he deems the identification of the patron of Athenæus Mechanicus with the conqueror of Syracuse to be unwarranted, and, besides, thinks it most unlikely that at so early a period a Greek should dedicate a work on military engines to any Roman. But from the expression employed by Athenæus, (ὦ σεμνότατε Μάρκελλε,) it may be inferred that his patron was a man of very exalted rank; and the second objection from the alleged improbability that a Greek should dedicate such a work to a Roman at that period will hardly be thought to apply at the period referred to, while the skill displayed by Marcellus in the siege of Syracuse, and the regret expressed by him for the fate of Archimedes, (whether genuine or not,) may well have suggested the dedication to him of a work on military engineering. The assumption of Fabricius, then, is, in itself, not to be too hastily rejected; and it will be seen that it is not so irreconcileable with the statement of Aristocles as has been supposed. Fabricius has carried back the date further than his argument requires or even warrants. Marcellus was killed B. C. 208: Athenæus might have inscribed his work to him about B. C. 212 or 210; at this period, then, we must suppose Ctesibius to have been known as a philosopher,[2] but he may have lived far into the succeeding century,—possibly even into the reign of Euergetes II. (B. C. 170–117); Hero would thus be placed about B. C. 150, a result by no means inconsistent with the statement of Aristocles, since it is not necessary, with Clinton, to assign the whole of the long reign of Euergetes II. to Ctesibius, and then to put Hero so low down as the reign of Ptolemy VIII.

The treatise on Pneumatics was first published in an Italian translation by Aleotti (Bologna, 1547). In 1575 appeared a Latin version by F. Commandine (Urbino, 1575): this translation, through which the work has been most extensively known, was reprinted at Amsterdam and at Paris. Several other translations were made into Italian, and one into German (see Fabricius, iv. p. 235). It was not till the year 1693, and subsequently to the appearance of all the versions named above, that the Greek text was published at Paris in the _Veterum Mathematicorum Opera_. The design of this collection was formed by Thevenot, deputy librarian of the Royal library in the reign of Louis XIV., and after his death it was carried out by De la Hire. Thevenot’s plan was to publish an accurate transcript of the MSS. of the several authors. The inevitable obscurity arising from the numerous corruptions which had crept into the manuscripts was to be remedied by an appendix of notes and a Latin translation. But for the Pneumatics of Hero it seemed sufficient to adopt the already well-known translation of Commandine; and, in consequence, of the eight MSS. of this treatise existing in the Royal Library, that one was chosen which most nearly agreed with the Latin version. This MS. was closely followed, and, as might be expected, the printed text is extremely corrupt: not unfrequently entire clauses are wanting, which, ending with the same word as the clause preceding, seem to have been passed over by the transcriber, whose eye, in returning from his copy to the original, rested on the second instead of the first of the two similar words. These defective passages, which appear to have been conjecturally restored by Commandine, have been supplied in the present translation from MSS. of Hero preserved in the British Museum. These MSS. are described in the appendix, where the most important cases in which the printed text has been supplemented, or otherwise amended, from this source are collected. When any words are included in the translation between brackets, it is to be understood that they appear neither in the text nor in any of the MSS. collated, but have been inserted as necessary to the sense.

The other treatises of Hero are:—1. On the construction of slings. 2. On the construction of missiles. 3. On automata. These are published in Greek and Latin in the _Vet. Math._ 4. On the method of lifting heavy bodies. This treatise has not yet been edited: it exists only in an Arabic translation. 5. On the “dioptra” or spying-tube: also inedited. It exists in manuscript in the Royal Library at Vienna, and among the MSS. of Hero contained in the Library of the University of Strasburgh. Schweighæuser in his notice of these MSS. (ap. Fabric. iv. p. 226), intimates that this treatise is of much interest, and contains an account of the dioptra “newly invented or improved by Hero himself.” Some help might perhaps be derived from it towards the settlement of Hero’s date, as the dioptra is mentioned and minutely commented on by Polybius. Several other treatises, entirely lost, are enumerated by Fabricius, iv. p. 236.

A question of great interest presents itself as to the claim of Hero to be considered as the inventor of the several machines and methods described by him. In the introduction of the “Pneumatica” he declares that his purpose is to arrange in order the discoveries of his predecessors, and to add to them his own. The treatise on the construction of missiles is ascribed in some MSS. to Ctesibius, (as in one at Leyden, Fabric. iv. p. 229,) while at the end of a MS. of the same work in the Library of Vienna are these words, τέλος τῶν Ἀρχιμήδους Βελοποιΐκῶν, τῶν ἐξηγηθέντων παρὰ Ἥρωνος Κτησιβίου. Again, it is singular that neither Pliny nor Vitruvius has any reference to Hero, though Ctesibius and his inventions are repeatedly mentioned. Vitruvius (x. 7) minutely describes a machine for raising water to a great height, which he expressly ascribes to Ctesibius; and in the following chapter he treats, at great length, of the construction of water-organs, yet without any notice of Hero. Both Pliny and Vitruvius expressly name Ctesibius as famous for his skill in the invention of pneumatic and hydraulic instruments. Pliny’s words are (vii. 38) “Laudatus est Ctesibius pneumatica ratione et hydraulicis organis repertis.” Vitruvius, (x. 7, compare also ix. 8,) after his description of the machine for raising water, says “Nec tamen hæc sola ratio Ctesibii fertur exquisita, sed etiam plures et variis generibus ab eo liquore pressionibus coacto spiritus efferre ab natura mutuatos effectus ostenduntur, uti merularum aquæ motu voces, atque engibata, quæ bibentia tandem movent sigilla, cæteraque quæ delectationibus oculorum et aurium usu sensus eblandiuntur.” He refers the curious to the commentaries of Ctesibius himself. How well this description of Ctesibius’ inventions suits the general character of those preserved by Hero, will be manifest at once. Vitruvius, as Schneider has pointed out,[3] seems to have had no knowledge of Hero’s Pneumatics, as both the forcing-pump and the water-organ differ in several important particulars from those of Hero: he does not even notice the application of the forcing-pump in extinguishing conflagrations. This silence on the part of Vitruvius and Pliny, so remarkable on the supposition that Hero was an original discoverer, is more easily accounted for if we regard him rather as the interpreter of Ctesibius.[4]

For further details on the life and writings of Hero, the reader is referred to Fabricius, iv. pp. 222–239, Smith’s Dictionary of Biography, and Baldi _de Vita Heronis_, in his edition of the Belopœica.

J. G. G.

Jan. 31, 1851.

FOOTNOTES:

[1] This has, indeed, been conjectured to be an error for Ἥρωνος ἢ Κτησιβίου, but Baldi (in his edition of the Belopœica, p. 44,) has satisfactorily proved that Hero was the writer.

[2] That Ctesibius began his researches at an early age may be inferred from the fact mentioned by Vitruvius, ix. 9. (edit. Schneider.)

[3] On Vitruvius, x. 7. The sections of Hero and the corresponding chapters of Vitruvius are minutely compared by Schneider, Vitruv. vol. iii. pp. 283–330.

[4] Baldi arrives at the same conclusion: (p. 74) “Cæterum haud immerito quispiam dubitaverit quam ob rem Architectus Heronis nostri nomen silentio præterierit. Nos ideo factum putamus quod ille Ctesibio utpote inventori ea tribuere maluerit quæ ab Herone locupletiora et illustriora quam ipse a magistro accepisset evulgata fuere.”

CORRIGENDA.

Page 4, line 3, _for_ them _read_ it.
14, figure. The mouth of the vessel should be open.
25, line 8, _for_ ⁷⁄₀₁ _read_ ⁷⁄₁₀.
35, .. 25, after P R, _read_ so that the goblet may be filled,
and the pedestal M N O X as high, &c.
40, .. 6, for _Wine and Water_ read _Wine-and-Water_.
—, figure. The pipe S T should connect the vessels A B and C D
near their bases.
43, line 23, _for_ across a third pulley, C, to another pulley, S,
_read_ across the pulley S to another pulley, T.
61, .. 12, _dele_ , _after_ vessel.
62, .. 7 }
—, .. 27 } _for_ the Hercules _read_ Hercules.
63, .. 6 }
79, .. 1, _dele_ , after _attached_.
84, .. 4, _read_ (from which extends the hand of the figure which
is to pour the libation.)
—, .. 6, _read_ side of the wine vessel.
89, .. 23, _for_ escaping _read_ entering.
96, .. 18, _dele_ , _after_ partition.
105, .. 6, _after_ this _insert_ and communicating with it.

CONTENTS.

Page

1. The bent Siphon 11

2. Concentric or inclosed Siphon 14

3. Uniform discharge Siphon 16

4. Siphon which is capable of discharging a greater or less
quantity of Liquid with uniformity 17

5. A Vessel for withdrawing Air from a Siphon 18

6. A Vessel for retaining or discharging a Liquid at pleasure 19

7. A Vessel for discharging Liquids of different temperatures at
pleasure 20

8. A Vessel for discharging Liquids in varying proportions 22

9. A Water Jet produced by mechanically compressed Air 23

10. A Valve for a Pump 25

11. Libations on an Altar produced by Fire 26

12. A Vessel from which the contents flow when filled to a certain
height 27

13. Two Vessels from which the contents flow, by a Liquid being
poured into one only 28

14. A Bird made to whistle by flowing Water 29

15. Birds made to sing and be silent alternately by flowing
Water 31

16. Trumpets sounded by flowing Water 32

17. Sounds produced on the opening of a Temple Door 33

18. Drinking-Horn from which either Wine or Water will flow 34

19. A Vessel containing a Liquid of uniform height, although a
Stream flows from it 35

20. A Vessel which remains full, although Water be drawn from it 36

21. Sacrificial Vessel which flows only when Money is introduced 37

22. A Vessel from which a variety of Liquids may be made to flow
through one Pipe 38

23. A Flow of Wine from one Vessel, produced by Water being poured
into another 39

24. A Pipe from which flows Wine-and-Water in varying
proportions 40

25. A Vessel from which Wine flows in proportion as Water is
withdrawn 41

26. A Vessel from which Wine flows in proportion as Water is
poured into another 43

27. The Fire-Engine 44

28. An Automaton which drinks at certain times only, on a Liquid
being presented to it 46

29. An Automaton which may be made to drink at any time, on a
Liquid being presented to it 47

30. An Automaton which will drink any quantity that may be
presented to it 48

31. A Wheel in a Temple, which, on being turned liberates
purifying Water 49

32. A Vessel containing different Wines, any one of which may be
liberated by placing a certain Weight in a Cup 50

33. A self-trimming Lamp 52

34. A Vessel from which Liquid may be made to flow, on any portion
of Water being poured into it 53

35. A Vessel which will hold a certain quantity of Liquid when the
supply is continuous, will only receive a portion of such
Liquid if the supply is intermittent 54

36. A Satyr pouring Water from a Wine-skin into a full
Washing-Basin, without making the contents overflow 55

37. Temple Doors opened by Fire on an Altar 57

38. Other intermediate means of opening Temple Doors by Fire on an
Altar 59

39. Wine flowing from a Vessel may be arrested on the Introduction
of Water, but, when the Supply of Water ceases, the Wine flows
again 60

40. On an Apple being lifted, Hercules shoots a Dragon which then
hisses 62

41. A Vessel from which uniform Quantities only of Liquid can be
poured 64

42. A Water Jet actuated by compressed Air from the Lungs 65

43. Notes from a Bird produced at intervals by an intermittent
Stream of Water 66

44. Notes produced from several Birds in succession, by a Stream
of Water 67

45. A Jet of Steam supporting a Sphere 68

46. The World represented in the Centre of the Universe 68

47. A Fountain which trickles by the Action of the Sun’s Rays 69

48. A Thyrsus made to whistle by being submerged in Water 70

49. A Trumpet, in the Hands of an Automaton, sounded by
compressed Air 71

50. The Steam-Engine 72

51. A Vessel from which flowing Water may be stopped at pleasure 73

52. A Drinking-Horn in which a peculiarly formed Siphon is fixed 74

53. A Vessel in which Water and Air ascend and descend
alternately 75

54. Water driven from the Mouth of a Wine-skin in the Hands of a
Satyr, by means of compressed Air 76

55. A Vessel, out of which Water flows as it is poured in, but if
the supply is withheld, Water will not flow again, until the
Vessel is half filled; and on the supply being again stopped,
it will not then flow until the Vessel is filled 77

56. A Cupping-Glass, to which is attached, an Air-exhausted
Compartment 79

57. Description of a Syringe 80

58. A Vessel from which a Flow of Wine can be stopped, by pouring
into it a small Measure of Water 81

59. A Vessel from which Wine or Water may be made to flow,
separately or mixed 82

60. Libations poured on an Altar, and a Serpent made to hiss, by
the Action of Fire 83

61. Water flowing from a Siphon ceases on surrounding the End of
its longer Side with Water 85

62. A Vessel which emits a Sound when a Liquor is poured from it 86

63. A Water-Clock, made to govern the quantities of Liquid flowing
from a Vessel 87

64. A Drinking-Horn from which a Mixture of Wine and Water, or
pure Water may be made to flow alternately or together, at
pleasure 89

65. A Vessel from which Wine or Water may be made to flow
separately or mixed 90

66. Wine discharged into a Cup in any required quantity 91

67. A Goblet into which as much Wine flows as is taken out 92

68. A Shrine over which a Bird may be made to revolve and sing by
Worshippers turning a Wheel 93

69. A Siphon fixed in a Vessel from which the Discharge shall
cease at will 94

70. Figures made to dance by Fire on an Altar 95

71. A Lamp in which the Oil can be raised by Water contained
within its Stand 96

72. A Lamp in which the Oil is raised by blowing Air into it 98

73. A Lamp in which the Oil is raised by Water as required 99

74. A Steam-Boiler from which a hot-Air blast, or hot-Air mixed
with Steam is blown into the Fire, and from which hot Water
flows on the introduction of cold 100

75. A Steam-Boiler from which either a hot Blast may be driven
into the Fire, a Blackbird made to sing, or a Triton to blow
a Horn 103

76. An Altar Organ blown by manual Labour 105

77. An Altar Organ blown by the agency of a Wind-mill 108

78. An Automaton, the head of which continues attached to the
body, after a knife has entered the neck at one side, passed
completely through it, and out at the other; the animal will
drink immediately after the operation 109

A TREATISE ON PNEUMATICS.

The investigation of the properties of Atmospheric Air having been deemed worthy of close attention by the ancient philosophers and mechanists, the former deducing them theoretically, the latter from the action of sensible bodies, we also have thought proper to arrange in order what has been handed down by former writers, and to add thereto our own discoveries: a task from which much advantage will result to those who shall hereafter devote themselves to the study of mathematics. We are further led to write this work from the consideration that it is fitting that the treatment of this subject should correspond with the method given by us in our treatise, in four books, on water-clocks. For, by the union of air, earth, fire and water, and the concurrence of three, or four, elementary principles, various combinations are effected, some of which supply the most pressing wants of human life, while others produce amazement and alarm.

But, before proceeding to our proper subject, we must treat of the vacuum. Some assert that there is absolutely no vacuum; others that, while no continuous vacuum is exhibited in nature, it is to be found distributed in minute portions through air, water, fire and all other substances: and this latter opinion, which we will presently demonstrate to be true from sensible phenomena, we adopt. Vessels which seem to most men empty are not empty, as they suppose, but full of air. Now the air, as those who have treated of physics are agreed, is composed of particles minute and light, and for the most part invisible. If, then, we pour water into an apparently empty vessel, air will leave the vessel proportioned in quantity to the water which enters it. This may be seen from the following experiment. Let the vessel which seems to be empty be inverted, and, being carefully kept upright, pressed down into water; the water will not enter it even though it be entirely immersed: so that it is manifest that the air, being matter, and having itself filled all the space in the vessel, does not allow the water to enter. Now, if we bore the bottom of the vessel, the water will enter through the mouth, but the air will escape through the hole. Again, if, before perforating the bottom, we raise the vessel vertically, and turn it up, we shall find the inner surface of the vessel entirely free from moisture, exactly as it was before immersion. Hence it must be assumed that the air is matter. The air when set in motion becomes wind, (for wind is nothing else but air in motion), and if, when the bottom of the vessel has been pierced and the water is entering, we place the hand over the hole, we shall feel the wind escaping from the vessel; and this is nothing else but the air which is being driven out by the water. It is not then to be supposed that there exists in nature a distinct and continuous vacuum, but that it is distributed in small measures through air and liquid and all other bodies. Adamant alone might be thought not to partake of this quality, as it does not admit of fusion or fracture, and, when beaten against anvils or hammers, buries itself in them entire. This peculiarity however is due to its excessive density: for the particles of fire, being coarser than the void spaces in the stone, do not pass through them, but only touch the outer surface; consequently, as they do not penetrate into this, as into other substances, no heat results. The particles of the air are in contact with each other, yet they do not fit closely in every part, but void spaces are left between them, as in the sand on the sea shore: the grains of sand must be imagined to correspond to the particles of air, and the air between the grains of sand to the void spaces between the particles of air. Hence, when any force is applied to it, the air is compressed, and, contrary to its nature, falls into the vacant spaces from the pressure exerted on its particles: but when the force is withdrawn, the air returns again to its former position from the elasticity of its particles, as is the case with horn shavings and sponge, which, when compressed and set free again, return to the same position and exhibit the same bulk. Similarly, if from the application of force the particles of air be divided and a vacuum be produced larger than is natural, the particles unite again afterwards; for bodies will have a rapid motion through a vacuum, where there is nothing to obstruct or repel them, until they are in contact. Thus, if a light vessel with a narrow mouth be taken and applied to the lips, and the air be sucked out and discharged, the vessel will be suspended from the lips, the vacuum drawing the flesh towards it that the exhausted space may be filled. It is manifest from this that there was a continuous vacuum in the vessel. The same may be shown by means of the egg-shaped cups used by physicians, which are of glass,[5] and have narrow mouths. When they wish to fill these with liquid, after sucking out the contained air, they place the finger on the vessel’s mouth and invert it into the liquid; then, the finger being withdrawn, the water is drawn up into the exhausted space, though the upward motion is against its nature. Very similar is the operation of cupping-glasses, which, when applied to the body, not only do not fall though of considerable weight, but even draw the contiguous matter toward them through the apertures of the body. The explanation is that the fire placed in them consumes and rarefies the air they contain, just as other substances, water, air or earth are consumed and pass over into more subtle substances.

That something is consumed by the action of fire is manifest from coal-cinders, which, preserving the same bulk as they had before combustion, or nearly so, differ very much in weight. The consumed parts pass away with the smoke into a substance of fire or air or earth: the subtlest parts pass into the highest region where fire is; the parts somewhat coarser than these into air, and those coarser still, having been borne with the others a certain space by the current, descend again into the lower regions and mingle with earthy substances. Water also, when consumed by the action of fire, is transformed into air; for the vapour arising from cauldrons placed upon flames is nothing but the evaporation from the liquid passing into air. That fire, then, dissolves and transforms all bodies grosser than itself is evident from the above facts. Again, in the exhalations that rise from the earth the grosser kinds of matter are changed into subtler substances; for dew is sent up from the evaporation of the water contained in the earth by exhalation; and this exhalation is produced by some igneous substance, when the sun is under the earth and warms the ground below, especially if the soil be sulphureous or bituminous, and the ground thus warmed increases the exhalation. The warm springs found in the earth are due to the same cause. The lighter portions of the dew, then, pass into air; the grosser, after being borne upwards for a certain space from the force of the exhalation, when this has cooled at the return of the sun, descend again to the surface.

Winds are produced from excessive exhalation, whereby the air is disturbed and rarefied, and sets in motion the air in immediate contact with it. This movement of the air, however, is not everywhere of uniform velocity: it is more violent in the neighbourhood of the exhalation, where the motion began; fainter at a greater distance from it: just as heavy bodies, when rising, move more rapidly in the lower region where the propelling force is, and more slowly in the higher; and when the force which originally propelled them no longer acts upon them, they return to their natural position, that is, to the surface of the earth. If the propelling force continued to urge them onward with equal velocity, they would never have stopped; but now the force gradually ceases, being as it were expended, and the speed of the motion ceases with it.

Water, again, is transformed into an earthy substance: if we pour water into an earthy and hollow place, after a short time the water disappears, being absorbed by the earthy substance, so that it mingles with, and is actually transformed into, earth. And if any one says that it is not transformed or absorbed by the earth, but is drawn out by heat, either of the sun or some other body, he shall be shewn to be mistaken: for if the same water be put into a vessel of glass, or bronze, or any other solid material, and placed in the sun, for a considerable time it is not diminished except in a very small degree. Water, therefore, is transformed into an earthy substance: indeed, slime and mud are transformations of water into earth.

Moreover, the more subtle substance is transformed into the grosser; as in the case of the flame of a lamp dying out for want of oil,—we see it for a time borne upwards and, as it were, striving to reach its proper region, that is, the highest of all above the atmosphere, till, overpowered by the mass of intervening air, it no longer tends to its kindred place, but, as though mixed and interwoven with the particles of air, becomes air itself. The same may be observed with air. For, if a small vessel containing air and carefully closed be placed in water with the mouth uppermost, and then, the vessel being uncovered, the water be allowed to rush in, the air escapes from the vessel; but, being overpowered by the mass of water, it mingles with it again and is transformed so as to become water.

When, therefore, the air in the cupping-glasses, being in like manner consumed and rarefied by fire, issues through the pores in the sides of the glass, the space within is exhausted and draws towards it the matter adjacent, of whatever kind it may be. But, if the cupping-glass be slightly raised, the air will enter the exhausted space and no more matter will be drawn up.

They, then, who assert that there is absolutely no vacuum may invent many arguments on this subject, and perhaps seem to discourse most plausibly though they offer no tangible proof. If, however, it be shewn by an appeal to sensible phenomena that there is such a thing as a continuous vacuum, but artificially produced; that a vacuum exists also naturally, but scattered in minute portions; and that by compression bodies fill up these scattered vacua, those who bring forward such plausible arguments in this matter will no longer be able to make good their ground.

Provide a spherical vessel, of the thickness of metal plate so as not to be easily crushed, containing about 8 cotylæ (2 quarts). When this has been tightly closed on every side, pierce a hole in it, and insert a siphon, or slender tube, of bronze, so as not to touch the part diametrically opposite to the point of perforation, that a passage may be left for water. The other end of the siphon must project about 3 fingers’ breadth (2 in.) above the globe, and the circumference of the aperture through which the siphon is inserted must be closed with tin applied both to the siphon and to the outer surface of the globe, so that when it is desired to breathe through the siphon no air may possibly escape from the vessel. Let us watch the result. The globe, like other vessels commonly said to be empty, contains air, and as this air fills all the space within it and presses uniformly against the inner surface of the vessel, if there is no vacuum, as some suppose, we can neither introduce water nor more air, unless the air contained before make way for it; and if by the application of force we make the attempt, the vessel, being full, will burst sooner than admit it. For the particles of air cannot be condensed, as there must in that case be interstices between them, by compression into which their bulk may become less; but this is not credible if there is no vacuum: nor again, as the particles press against one another throughout their whole surface and likewise against the sides of the vessel, can they be pushed away so as to make room if there is no vacuum. Thus in no way can anything from without be introduced into the globe unless some portion of the previously contained air escape; if, that is to say, the whole space is closely and uniformly filled, as the objectors suppose. And yet, if any one, inserting the siphon in his mouth, shall blow into the globe, he will introduce much wind without any of the previously contained air giving way. And, this being the uniform result, it is clearly shewn that a condensation takes place of the particles contained in the globe into the interspersed vacua. The condensation however is effected artificially by the forcible introduction of air. Now if, after blowing into the vessel, we bring the hand close to the mouth, and quickly cover the siphon with the finger, the air remains the whole time pent up in the globe; and on the removal of the finger the introduced air will rush out again with a loud noise, being thrust out, as we stated, by the expansion of the original air which takes place from its elasticity. Again, if we draw out the air in the globe by suction through the siphon, it will follow abundantly, though no other substance take its place in the vessel, as has been said in the case of the egg. By this experiment it is completely proved that an accumulation of vacuum goes on in the globe; for the particles of air left behind cannot grow larger in the interval so as to occupy the space left by the particles driven out. For if they increase in magnitude when no foreign substance can be added, it must be supposed that this increase arises from expansion, which is equivalent to a re-arrangement of the particles through the production of a vacuum. But it is maintained that there is no vacuum; the particles therefore will not become larger, for it is not possible to imagine for them any other mode of increase. It is clear, then, from what has been said that certain void spaces are interspersed between the particles of the air, into which, when force is applied, they fall contrary to their natural action.

The air contained in the vessel inverted in water does not undergo much compression, for the compressing force is not considerable, seeing that water, in its own nature, possesses neither weight nor power of excessive pressure. Whence it is that, though divers to the bottom of the sea support an immense weight of water on their backs, respiration is not compelled by the water, though the air contained in their nostrils is extremely little. It is worth while here to examine what reason is given why those who dive deep, supporting on their backs an immense weight of water, are not crushed. Some say that it is because water is of uniform weight: but these give no reason why divers are not crushed by the water above. The true reason may be shewn as follows. Let us imagine the column of liquid which is directly over the surface of the object under pressure, (in immediate contact with which the water is,) to be a body of the same weight and form as the superincumbent liquid, and that this is so placed in the water that its under surface coincides with the surface of the body pressed, resting upon it in the same manner as the previously superincumbent liquid, with which it exactly corresponds. It is clear, then, that this body does not project above the liquid in which it is immersed, and will not sink beneath its surface. For Archimedes has shewn, in his work on ‘Floating Bodies,’ that bodies of equal weight with any liquid, when immersed in it, will neither project above nor sink beneath its surface: therefore they will not exert pressure on objects beneath. Again, such a body, if all objects which exert pressure from above be removed, remains in the same place; how then can a body which has no tendency downward exert pressure? Similarly, the liquid displaced by the body will not exert pressure on objects beneath; for, as regards rest and motion, the body in question does [not] differ from the liquid which occupies the same space.

Again, that void spaces exist may be seen from the following considerations: for, if there were not such spaces, neither light, nor heat, nor any other material force could penetrate through water, or air, or any body whatever. How could the rays of the sun, for example, penetrate through water to the bottom of the vessel? If there were no pores in the fluid, and the rays thrust the water aside by force, the consequence would be that full vessels would overflow, which however does not take place. Again, if the rays thrust the water aside by force, it would not be found that some were reflected while others penetrated below; but now all those rays that impinge upon the particles of the water are driven back, as it were, and reflected, while those that come in contact with the void spaces, meeting with but few particles, penetrate to the bottom of the vessel. It is clear, too, that void spaces exist in water from this, that, when wine is poured into water, it is seen to spread itself through every part of the water, which it would not do if there were no vacua in the water. Again, one light traverses another; for, when several lamps are lighted, all objects are brilliantly illuminated, the rays passing in every direction through each other. And indeed it is possible to penetrate through bronze, iron, and all other bodies, as is seen in the instance of the marine torpedo.

That a continuous vacuum can be artificially produced has been shewn by the application of a light vessel to the mouth, and by the egg of physicians. With regard, then, to the nature of the vacuum, though other proofs exist, we deem those that have been given, and which are founded on sensible phenomena, to be sufficient. It may, therefore, be affirmed in this matter that every body is composed of minute particles, between which are empty spaces less than the particles of the body, (so that we erroneously say that there is no vacuum except by the application of force, and that every place is full either of air, or water, or some other substance), and, in proportion as any one of these particles recedes, some other follows it and fills the vacant space: that there is no continuous vacuum except by the application of some force: and again, that the absolute vacuum is never found, but is produced artificially.

These things having been clearly explained, let us treat of the theorems resulting from the combination of these principles; for, by means of them, many curious and astonishing kinds of motion may be discovered. After these preliminary considerations we will begin by treating of the bent siphon, which is most useful in many ways in Pneumatics.

FOOTNOTES:

[5] “Glass working was practised by the ancient Egyptians at a very early period of their national existence. Sir J. G. Wilkinson, in his able work on the _Manners and Customs of the ancient Egyptians_, has adduced three distinct proofs that the art of Glass working was practised in Egypt before the Exodus of the children of Israel from that land, three thousand five hundred years ago. At Beni Hassan are two paintings representing Glass blowers at work, and from the hieroglyphics accompanying them they are shown to have been executed in the reign of the first Osirtasen at the early date above mentioned. Such was the skill of the Egyptians in glass making, that they successively counterfeited the Amethyst and other precious stones worn as ornaments for the person. Winckelmann, a high authority, is of opinion that glass was employed more frequently in ancient than in modern times; it was used by the Egyptians even for coffins; (_within the year 1847 a process was patented in England for making Coffins of Glass_) they also employed it not only for drinking vessels but for Mosaic work, the figures of deities, and sacred emblems, in which they attained excellent workmanship, and surprising brilliancy of colour. “It is certain that the glass houses of Alexandria were celebrated among the ancients for the skill and ingenuity of their workmen; and from thence the Romans, who did not acquire a knowledge of the art till a later period, procured all their Glass ware.

“Most of the large cinerary vases in the British Museum, found in Roman barrows which contained bones and bone-ashes, are, probably, the production of extensive Egyptian or Roman works: they are large, and of excellent form and workmanship: but the Glass is somewhat impure, of a greenish tint, has numerous globules and striæ, and is not unlike the modern common crown or sheet glass in quality.

“We have incidentally mentioned the discovery of Glass at Pompeii. Glass vessels have also been found among the ruins of Herculaneum: and it appears that Glass was used for admitting light to dwellings in Pompeii.

“Mr. Auldjo, of Noel house, Kensington, who resided several years at Naples, states, that he has seen glass in the window-frames of some of the houses of Pompeii.

“Mr. Roach Smith has a specimen of ancient flat Glass such as he believes to have been used by the Romans, or their predecessors for windows.”—_Curiosities of Glass making by_ APSLEY PELLAT, London, 1849.

Mr. Layard in his interesting work on Nineveh, 1849, London, in Vol. I, page 342, says: “I took the instrument, and, working cautiously myself, was rewarded by the discovery of two small vases, one in alabaster, the other in glass (both in the most perfect preservation) of elegant shape, and admirable workmanship. Each bore the name and title of the Khorsabad King, written in two different ways, as in the inscriptions of Khorsabad.”

_No. 1. The bent Siphon._

Let A B C, (fig. 1), be a bent siphon, or tube, of which the leg A B is plunged into a vessel D E containing water. If the surface of the water is in F G, the leg of the siphon, A B, will be filled with water as high as the surface, that is, up to H, the portion H B C remaining full of air. If, then, we draw off the air by suction through the aperture C, the liquid also will follow from the impossibility, explained above, of a continuous vacuum. And, if the aperture C be level with the surface of the water, the siphon, though full, will not discharge the water, but will remain full: so that, although it is contrary to nature for water to rise, it has risen so as to fill the tube A B C; and the water will remain in equilibrium, like the beams of a balance, the portion H B being raised on high, and the portion B C suspended. But if the outer mouth of the siphon be lower than the surface F G, as at K, the water flows out; for the liquid in K B, being heavier, overpowers and draws toward it the liquid in B H. The discharge, however, continues only until the surface of the water is on a level with the mouth K, when, for the same reason as before, the efflux ceases. But if the outer mouth of the tube be lower than K, as at L, the discharge continues until the surface of the water reaches the mouth A. If then we wish all the water in the vessel to be drawn out, we must depress the siphon so far that the mouth A may reach the bottom of the vessel, leaving only a passage for the water.

Now some writers have given the above explanation of the action of the siphon, saying that the longer leg, holding more, attracts the shorter. But that such an explanation is incorrect, and that he who believes so would be greatly mistaken if he were to attempt to raise water from a lower level, we may prove as follows. Let there be a siphon with its inner leg longer and narrow, and the outer much less in length but broader so as to contain more water than the longer leg. Then, having first filled the siphon with water, plunge the longer leg into a vessel of water or a well. Now, if we allow the water to flow, the outer leg, containing more than the inner, should draw the water out of the longer leg, which will at the same time draw up the water in the well; and the discharge having begun will exhaust all the water or continue for ever, since the liquid without is more than that within. But this is not found to be the case; and therefore the alleged cause is not the true one. Let us then examine into the natural cause. The surface of every liquid body, when at rest, is spherical and concentric with that of the earth; and, if the liquid be not at rest, it moves until it attains such a surface. If then we take two vessels and pour water into each, and, after filling the siphon and closing its extremities with the fingers, insert one leg into one vessel plunging it beneath the water, and the other into the other, all the water will be continuous, for each of the liquids in the vessels communicates with that in the siphon. If, then, the surfaces of the liquids in the vessels were at the same level before, they will both remain at rest when the siphon is plunged in. But if they were not, as soon as the water is continuous it must inevitably flow into the lower vessel through the channel of communication, until either all the water in both vessels stands at the same height, or one of the vessels is emptied. Suppose that the liquids stand at the same height; they will of course be at rest, so that the liquid in the siphon will also be at rest. If, then, the siphon be conceived to be intersected by a plane in the surface of the liquids in the vessels, even now the liquid in the siphon will be at rest, and, if raised without being inclined to either side, it will again be at rest, and that, whether the siphon is of equal breadth throughout or one leg is much larger than the other. For the reason why the liquid remained at rest did not lie in this, but in the fact that the apertures of the siphon were at the same level. The question now arises why, when the siphon is raised, the water is not borne down by its own weight, having beneath it air which is lighter than itself. The answer is that a continuous void cannot exist; so that, if the water is to descend, we must first fill the upper part of the siphon, into which no air can possibly force its way. But if we pierce a hole in the upper part of the siphon, the water will immediately be rent in sunder the air having found a passage. Before the hole is bored, the liquid in the siphon, resting on the air beneath, tends to drive it away, but the air having no means of escape does not allow the water to pass out: when however the air has obtained a passage through the hole, being unable to sustain the pressure of the water, it escapes. It is from the same cause that, by means of a siphon, we can suck wine upwards, though this is contrary to the nature of a liquid; for, when we have received into the body the air which was in the siphon, we become fuller than before, and a pressure is exerted on the air contiguous to us, and this in turn presses on the atmosphere at large, until a void has been produced at the surface of the wine, and then the wine undergoing pressure itself will pass into the exhausted space of the siphon; for there is no other place into which it can escape from the pressure. It is from this cause that its unnatural upward movement arises.

That the water in the siphon will rest when its surface is spherical and concentric with that of the earth may be shewn otherwise. It is required to prove that a liquid is stationary when its surface is spherical and concentric with that of the earth. If possible let it not be stationary; it will of course become so after being moved; let it then have become stationary. Its surface will now be spherical and concentric with that of the earth, and it will cut the former surface; for, when the same liquid has taken two positions, there must be a line of intersection common to both. Let both surfaces be cut by a plane passing through the centre of the earth; the intersections will be the circumferences of circles concentric with the earth. Let these circumferences be A B C and F B D, (fig. 1 a.) Join B G; B G is equal to each of the lines G F, G A, which is absurd. The liquid will therefore be in equilibrium.

2. _Concentric or inclosed Siphon._