quently referred to in Pepys' Diary. Between them, however, they could not succeed in fashioning a serviceable machine, and Boyle had recourse to Robert Hooke, then a youth of some three and twenty, but already remarkable for his mechanical genius. No drawing of Greatorex's contrivance has been preserved; but Hooke, who had seen it, says of it, in his cutting way, that it "was too gross to perform any great matter."

full of air, with a syringe or pump, exactly | sistance of Greatorex, or Gratorix, a wellidentical in construction with one of the known instrument-maker of the time, freforms of the ordinary lift, or sucking pump, and found that by setting the piston in motion, he could empty the globe of air. He proceeded to make a number of interesting experiments, which added largely to men's knowledge of the properties of air, and have made his name and the city of his residence famous in every quarter of the civilized world. So many were the visitors that crowded to Guericke's house to witness his marvellous performances, that he had a large pump erected in his cellar, with tubes ascending into an upper room, and connected with suitable apparatus. At great receptions, the pump was driven all day by two men who kept emptying a very large copper globe of air. When an experiment was to be made, a communication was opened between this globe and the interior of much smaller vessels, the air contained in which was immediately greatly rarefied, and their cavities. left nearly vacuous. Were this the proper place, we should have much to say in praise of Otto von Guericke.

The fame of the Magdeburgh experiments soon reached England, and interested no one there so much as Boyle. He had been meditating, like Guericke, on Torricelli's results, and was considering how best a vacuum might be produced on the large scale, when he learned that he had been anticipated. He would probably have succeeded in his schemes, and the likelihood of this, along with the certainty that Boyle had endeavored to construct an air-pump before 1569, has led the late Professor Robison, the writer of the able article in the "Encyclopædia Britannica," on Pneumatics, to claim for Boyle the merit of being an independent, though not the first inventor of the air-pump. "Boyle," he says, "invented his air-pump, and was not indebted for it to Schottus's account of Otto Von Guericke's, published in the Mechanica Hydraulo-Pneumatica of Schottus, in 1657, as he asserts, Technica Curiosa." (Enc. Br., Art. Pneumaties, p. 72.) This is complimenting Boyle at Guericke's expense, in an uncalled-for way. The former, who was eminently free from envy, meanness, or jealousy, explicitly declares in a letter to his nephew, Lord Dungarvan, of date 1659, that he did not set about the construction of an air-pump till he had heard of Guericke's way of emptying glass vessels, by sucking out the air at the mouth of the vessel." Encouraged by the report of Guericke's success, Boyle called in the as

66

At this point, the history of the air-pump in England begins. Statements, the most erroneous and contradictory, occur in the works of writers of the highest authority, nor do we know any treatise which gives an accurate account of the steps in the invention and improvement of the machine, or which rightly marks the parties by whom they were made.

Men so eminent as Dr. Thomas Young, and Professor Baden Powell, have misled authorities of less esteem in this matter. Professor Robison, in addition to other mistakes, in his "Treatise on Pneumatics,' (Encyclopædia Britannica,) attributes one most important improvement (the double barrel) in one place to Hooke, and in another place to Hauksbee. Mr. Weld has completed the confusion, by announcing in his history, that the Royal Society has in its possession an ancient air-pump, once the property of Boyle, which is totally unlike any instrument figured or described in his works. It is time to set this matter to rights, and it may be well to remind the reader that, although the air-pump was invented in Germany, nearly all its great improvements have been made in England.

Greatorex's contrivance having been thrown aside, Hooke constructed for Boyle, in 1658 or 1659, the air-pump, with which his first series of pneumatic researches was made. The merit of devising this instrument should seem to be almost entirely Hooke's. Boyle at least claims very little to himself. His account of his first air-pump is contained in his treatise, entitled, "New Experiments, Physico-Mechanical, touching the spring of the Air and its effects, made, for the most part, in a new Pneumatical Engine; written by way of Letter to the Right Honorable Charles, Lord Viscount Dungarvan, eldest son of the Earl of Cork." The date of the letter is 1659. It is reprinted in Birch's Boyle, vol. i. Boyle mentions that he put both Mr. G. (Greatorex) and R. Hooke to

contrive an air-pump which should be more manageable than the German one, and free from its defects; and then adds, "after an unsuccessful trial or two, of ways proposed by others, the last-named person (R. Hooke) fitted me with a pump, anon to be described." (Birch's Boyle, vol. i. p. 7.) In a manuscript which was not published till after his death, Hooke himself says, "in 1658 or '9 I contrived and perfected the air-pump for Mr. Boyle." (Waller's Life of Hooke, p. 3.)

472.

the second volume of Shaw's Boyle, p.
It was necessary to describe it somewhat
minutely, for a reason which will presently
appear. The most important points to be
noticed about it are, that unlike any later air-
pump, the cylinder and the receiver were
directly connected, and, further, that it was
provided with only one barrel or pump. It
appears to have been partly in reference to
the former of those peculiarities, but also be-
cause he did not pretend to be able to pro-
duce an absolute vacuum, that Boyle named
his instrument. He seldom calls it an
air-pump. Once he speaks of Guericke's
instrument as "the wind-pump, as some-
body not improperly calls it." "Pneumatic
pump" also but rarely occurs. The title he
preferred for his instrument was that of
pneumatical engine." Others called it the
rarefying engine," and it was known over
Europe as Machina Boyleana-Boyle's ma-
chine.

This instrument consisted of two principal parts, a glass vessel, and a pump to draw the air out of it." The pump was so placed on a wooden tripod, as to have its mouth downwards, so that the piston-rod, or shank of the sucker, when, like the ramrod of a musket it was pushed home, ascended into the cylinder" or barrel. The object of this invention was to allow the glass vessel, from which it emptied the air, to be placed in a vertical position above the pump. This glass vessel Boyle called the receiver, an apparently paradoxical title for a hollow globe, which was, if possible, to be emptied of its original contents, atmospheric air. The name, however, which is still retained, though modern air-pump receivers are differently constructed, was eminently significant, and marked an important difference between Boyle's airpump, and Otto von Guericke's.

The receiver was a globe, or rather a pear-shaped vessel, with a large aperture at its wider upper end, provided with an air-tight movable cover. Through this aperture the vessel could be made to receive any object, such as a burning candle, or a living animal, on which it was intended to try the effects of a vacuum. The hollow stalk of the pearshaped receiver terminated in a brass tube, provided with a stop-cock, and ground to fit into the upper end of the inverted cylinder. The latter had an opening in it close to the place where the stop-cock entered, which could be closed or opened by a brass plug, ground to fit it, and managed by the hand of the experimenter, or the worker of the pump. The piston, which had no aperture or valve in it, was not moved directly by the hand. The piston-rod had teeth cut on it at one side, so as to form a rack, which was raised or depressed by a handle acting on a pinion or toothed wheel, working into the teeth of the rack, as in the air-pumps of the present day. We shall not dwell more minutely on the peculiarities of the original English air-pump. An engraving of it will be found at the end of the first volume of Birch's Boyle, and in

It was strictly a pneumatical, not a rarefying engine. It could be used to condense air into the globular receiver, as well as to withdraw air from it, as Boyle showed, and was thus something else than a mere vacuumproducer. Vapors and gases could also be introduced into the globe, as they were, in many of the experiments made with it. It was thus best denominated an air or pneumatical engine.

At the present day it would be considered an awkwardly contrived, ill-proportioned, and imperfect instrument. It taught Boyle, however, and his contemporaries so much, achieved such wonders, was so difficult of construction, and so costly, that its possessor called it his "Great" Pneumatical Engine. He did not retain it long in his possession. With a rare and noble liberality, he presented it to the Royal Society in 1662, so that his poorer scientific brethren, who could not afford so expensive a piece of apparatus, might study pneumatics at his cost, and multiply experiments by means of the great engine. Acts as liberal have been done by many men on their death-beds, but seldom during their life-time; and wealthy philosophers have rarely descended from the height of advantage their riches gave them, to put into poor men's hands the means of rivalling and outstripping them in their favorite pursuits.

For six or seven years Boyle turned aside from pneumatic research altogether, and no one took his place, at least in Great Britain. Finding that few new experiments had been made in the course of many years, he resumed his inquiries into the properties of the air,

and began by constructing a new air-pump. | of plate-glass; and the bell-jar receivers are His account of this, which he distinguishes as whelmed on upon the air-pump plate, as they his "Second Engine," and of the experiments were in Boyle's day. One great advantage which he made with it, was published in the of this arrangement was the increased stabilishape of a letter to his nephew, Lord Dun- ty given to the apparatus, by transferring garvan, entitled "A Continuation of New the heavy glass receiver, which in the first Experiments, Physico-Mechanical, touching air-pump was fixed by a narrow tube to the the spring and weight of the air, &c. &c, barrel, to a flat support, on which it rested Oxford 1669." The letter is dated March 24, on a broad base. Another advantage was 1667, which we may consider the year in the avoidance of many apertures, which could which the second English air-pump was con- not be kept air-tight, so that air should not structed, though it may have been finished leak into the receiver. For it must be rein the preceding year. Various considera- membered, that every pneumatic receiver, or tions "invited me,' says Boyle, "to make other exhausted vessel, lies at or near the some alterations in the structure, some of bottom of a deep sea of air, as a diving-bell them suggested by others, (especially the does at the bottom of a sea of water; and ingenious Mr. Hooke,) and some that I added the latter does not more readily rush into the myself, as finding that without them I could bell, through the smallest fissure, than air not do my work." forces its way along the most imperceptible channel, into the exhausted receiver. In the diving-bell there is air, at least, to resist the intrusion of water; but in the receiver there is a vacuum, soliciting the entrance of air. The fewer, therefore, the valves and stopcocks, the greater the chance of producing and preserving a good vacuum. A third advantage, to mention no more, was the facility which the plate afforded for placing on it any object, such as a candle, a barometer, a thermometer, a piece of clockwork, a growing plant, or the like; and when the object was exactly arranged, bell-jars, of various dimensions and shapes, could be laid over it, and the pump set working. In the first pneumatical engine, bodies intended to be subjected to a vacuum were awkwardly inserted by a large aperture at the top of the receiver, or suspended within it by strings,

The second pneumatical engine, like the first, had a single barrel; but the mouth of the latter, from which the piston-rod projected, was turned upwards, and the barrel stood in a wooden box, or trough, filled with water, which rose above the mouth of the cylinder, so that the latter was entirely under water. The object of this arrangement was to keep the leather of the piston, or sucker, always wet, and, as a consequence, "turgid and plump," so that it should move air-tight in the barrel. The piston, which was moved by a rack and pinion, had an aperture in it, which was closed and opened alternately, by thrusting in and pulling out a long stick, managed by the hand of the operator. But the great peculiarity and improvement in the engine was, that the receiver was not directly attached to the barrel. A tube, provided with a stop-cock, passed from the upper part of the side of the barrel, in a horizontal direction, along a groove, in a wooden board, covered by a thick iron plate, and was then bent up so as barely to project through the iron. The receiver was no longer a globe, or pear-shaped vessel, with various leaky apertures in it, but a bell-shaped, hollow, glass jar, which, turned with its mouth downwards, like an inverted drinking-glass, was, to use Boyle's homely but expressive words, "whelmed on upon the plate, well covered with cement." When the pump was wrought, the air in the bell-jar, or receiver, was drawn out through the horizontal tube. The reader familiar with pneumatics will recognize in the whole arrangement, a device which has been followed, with trifling alterations, in every later air-pump, down to the present day. Every modern air-pump has its "plate," made, however, not of iron, but of brass, or

Boyle published the account of the experiments he made with his second air-pump in 1669, and laid pneumatics again almost entirely aside for seven or eight years. In 1676, however, he began to think of resuming the subject; and he was fixed in his resolution by a visit paid him by a very ingenious and inventive Frenchman, Denis Papin, whose name is still connected with one of his many devices, the Bone-Digester, a peculiar high-pressure steam-boiler, with which he effected strange triumphs in cookery. He has a place, and a high one, long overlooked, among the inventors of the steamengine; and it will presently appear that he has a claim, also overlooked, to a high place among the inventors of the air-pump. Papin came to England in search of some situation which might afford scope for his mechanical genius. Boyle had lost the services of Hooke, whom he generously released from his en

gagements with him, in 1662, in order that he might become Curator and Experimenter to the Royal Society. Papin, for a time, became assistant to Boyle, whose indifferent health prevented him from experimenting much himself, and a new series of pneumatic researches was undertaken. This was the more readily accomplished, that Papin had brought with him "a pneumatic pump of his own, made by himself," and much superior in efficacy to either of Boyle's pneumatical engines.

An engraving and minute description of Papin's air-pump are given in Boyle's tract, entitled, "A Continuation of New Experiments, Physico-Mechanical, touching the spring and weight of the Air, and their Effects, Second Part." The substance of this tract was first noted down in French, by Papin, who performed most of the experiments; then translated by Boyle, or under his superintendence, into Latin, in which the treatise was first published. Afterwards, this was translated, under Boyle's supervision, into English, in which it is reprinted in Birch's Boyle, vol. iv. p. 504. We cannot give the original date of the Latin or English editions of the tract, which must be regarded as the joint production of Boyle and Papin, but the experiments recorded in it are all dated. The first bears date July 11, 1676, (B. B. iv. 519,) the last, February 17, 1679, (B. B. iv. 593.) Papin's air-pump, which he brought with him, is, therefore, at least as old as 1676, which may be considered the date of its introduction into England. Its great peculiarity, as contrasted with former air-pumps, was, that it had two barrels. It was, according to Boyle, Papin's own contrivance. The former, referring to the use he made of the latter's mechanical devices in prosecuting his researches, says: "Not a few of the mechanical instruments, (especially the double pump and wind-gun,) which sometimes were of necessary use to us in our work, are to be referred to his invention, who also made some of them, at least in part, with his own hands." (B. B. iv. 506.)

should seem, by his hands, to the upper part of the frame-work of the pump, or leaning against it, (for the description is not precise on this particular,) moved his feet alternately up and down, as a hand-loom weaver does, or a culprit on the treadmill. The pistons, or suckers, which were bottomless brass cylinders, had valves opening upwards, like that of an ordinary water-pump; and similar valves were placed at the bottom of the cylinders, which were filled with water to a certain height, that the pistons might move air-tight in them. From the cylinders, tubes passed to a common canal, terminating in the airpump plate, on which receivers to be exhausted were laid, as in Boyle's second engine.

The advantages of Papin's arrangement were very great. When a single pump is used, it becomes increasingly difficult, as the exhaustion proceeds, to draw out the piston against the pressure of the external air, which comes, towards the end, to oppose an unresisted force, equal to nearly fifteen pounds on each square inch, to the extrusion of the piston. When the piston, on the other hand, is pushed home, it is driven into the barrel with the same force which resists its withdrawal, and is liable to break the valves, or injure the bottom of the cylinder. But if the pistonrods of adjoining cylinders are balanced against each other, as those in Papin's machine were, so that the one ascends as the other descends, the evils described are all obviated. The resistance which the air offers to the ascent of the one piston is balanced, or nearly so, by the force with which it compels the other piston to descend, so that the two hang against each other almost in equilibrio. A very slight expenditure of force, accordingly, little more than is requisite to overcome the friction of the moving parts, suffices for the working of the pump. A double-barrelled air-pump not only exhausts twice as expeditiously as a single-barrelled one, but does double work for nearly the same expenditure of force. In this respect there is an essential difference between a double-barrelled airpump and a double-barrelled gun. In the Papin's air-pump was a curious machine; latter, a double effect is gained only at the it had two pumps standing side by side, the expense of a double expenditure of time and mouths of the barrels being turned upwards. force. Two gun-barrels require twice the Each of the piston-rods terminated in a stir- charge, loading, ramming, priming, and firing rup, attached to its upper end, and the stir- of one barrel, and take twice the time to load. rups were connected by a rope or cord, which In the air-pump, on the other hand, the workpassed over a vertical grooved wheel, or ing of the one piston renders much more easy large pulley, fixed on a movable axis. To the work of the other, and diminishes the work the machine, the exerciser of the pumps, time requisite for working both. The barrels as he is called in the original account, put his of a musket are isolated, though lying side feet into the stirrups, and holding on, as it by side, and are not mutually dependent;

or to Hauksbee, an admirable observer and very ingenious mechanician, who flourished in the first decade of the eighteenth century. Professor Baden Powell, in his interesting History of Natural Philosophy (p. 235) says, "Boyle made the first improvement, and reduced the air-pump to nearly its present construction." So general a statement, in a brief popular treatise, would not in itself, perhaps, call for criticism. It is quoted, however, by Mr. Weld, and has contributed, along with other things, to mislead him into a curious error, which, if uncontradicted, will propagate a grave mistake. The point of Professor Powell's statement lies in the word " nearly." In our judgment, he uses it with much too great a latitude. Boyle's two pneumatical engines were awk

but the pistons of the air-pump are, as it were, organically connected, like twins, and aid each other's movements. The peculiarity of Papin's device would have been more apparent, if his machine had been called, not the double-barrelled, but the twin-piston airpump. The twin-pistons were not the only advantage of Papin's pump; its valves were opened and shut by the air which passed through the apertures they covered, so that the valves were self-acting, like those of a water-pump. If the pistons were only kept alternately ascending and descending, nothing else was needed for the working of the machine. In Boyle's pneumatical engines, on the other hand, in addition to the labor of working the pump, the operator had, at every stroke of the piston, to shut a stopcock and thrust in a plug, or to open a stop-ward in construction, and without self-acting cock and pull out a plug. His engines, therefore, could not be wrought swiftly.

It is not a little singular, that Papin's airpump should have been overlooked by most later inventors and writers, at least in England. We have not found it referred to in any recent work of authority, although its curious stirrup-arrangement, which has been employed in no English air-pump, might have been expected to attract attention towards it. Papin is mentioned by Nairne, incidentally, as an improver of the air-pump, (Phil. Trans. 1777, p. 635.) Dr. Hutton, in his Mathematical Dictionary, (1796, vol. i, p. 55,) mentions Papin's two barrels and twinpistons, but not the stirrup-arrangement. In Shaw's Boyle the whole machine is described and figured, but Papin's name is not once mentioned; an omission which, at the present day, would be considered inexcusable in an editor or abridger. The double pump must pass, with Shaw's readers, for an invention of Boyle's; yet even the latter's great name has not kept the double-barrelled stirrup airpump in remembrance-a significant proof how little Boyle's works, even when abridged, are read by the very historians of his labors. It is in connection with the double-barrelled air-pump that the accepted history of the instrument is chiefly erroneous, but the mistakes made in reference to the more complex engine, have ultimately involved in confusion even the authentic records of the steps by which the earlier single-barrelled pump was improved. Recent writers on pneumatics, having overlooked Papin's machine, whilst they universally acknowledge the importance of two barrels with the pistons counterbalanci g each other, have attributed this great impro cment to Boyle, to Hooke,

or mechanical valves. They could not be wrought swiftly, and they produced only an imperfect vacuum. Boyle himself ingenuously and ungrudgingly acknowledges, that Guericke's pumps exhausted better than his. In compliment to his beautiful pneumatic researches, the whole of Europe, designedly passing by the prior claims of the burgomaster of Magdeburgh, called the air-pump vacuum, " Vacuum Boylianum." Boyle accepted the name, not as a compliment, but as a designation of what he intended when he used the word vacuum in his treatises. It referred to something between an absolute plenum and an absolute vacuum. It approached to the latter, but fell short of it. It was not Nature's vacuum, the thing she so much abhorred, but Boyle's vacuum, the best that the Honorable Robert Boyle could produce with his pneumatical engines. It seems well to notice, although it is a digression, lest we should be thought to have forgotten our duty as biographers, that those things are not pointed out to disparage the genius of the great philosopher. Professor Powell's statement lessens instead of exalting Boyle's claims to our admiration. His merit lies not in having constructed a perfect airpump, but in having made an excellent use of a very imperfect one. There is a wellknown class of painters who are always wandering about in search of "a good light," whilst Wilkies are completing great pictures in dim garrets. There is an equally wellknown class of natural philosophers, forever roving from mechanician to mechanician in search of better instruments; while others are discovering new planets, new living beings, or new elements, by apparatus which their dissatisfied brethren can demonstate to