426 Guerricke's Illustration of Atmospheric Pressure . [Book IV.

may be thought of engines made previous to the 17th Century, those ofmodern days were obviously derived from atmospheric ones of the firstdass, while these in their turn were very likely deduced from the appa-ratus described in the next paragraph.

Otto Guerricke, of whom we spoke at page 190, one of the earliest, andas far as mechanical ingenuity went perhaps the most gifted, of the early

elucidators of atmospheric pressure,exhibited in his public experimentsat Ratisbon , in 1654, the followingapplication of that pressure as a mo-tive force. A large cylinder, A, wasfirmly secured to a post or frame,It was open at the top and closed atthe bottom, and had a piston accu-rately fitted to work in it. A ropewas fastened tt> the piston-rod andpassed over two pulleys, B C, as rep-resented, by which was suspended ascale, D, containing several weights.When the air was withdrawn fromthe lower part of the cylinder, thepressure of the atmosphere depress-ed the piston and raised the scale andweights. To vary the experiment,the weights were removed andtwenty men were employed to pullat the rope with all their strength;but as soon as a vacuum was made by the small air-pump attached to thebottom of the cylinder, the piston descended, notwithstanding all theirefforts to prevent it.

This is the oldest apparatus on record for transmitting motion to solidsby a piston. We can however hardly believe that it was the first devisedfor the purpose. It would be stränge if it were ; for whatever may havebeen the nature of Anthemius ’s, Garay’s, and other old machines inwhich steam was the active principle, pumps and syringes had been toocommon, and experiments with them too frequent, for such a device tohave been unknown. Such men as Aristotle and Archimedes, Ctesibius ,Heron, Roger Bacon and their successors, were all aware that a syringepresented the same phenomenon as Guerricke’s apparatus, when the pis-ton was drawn up while the discharging orifice was closed : the samething was also observed with common pumps when the suction-pipes wereeither closed or choked. Experiments therefore to illustrate the forcethus excited were in all probability made, and with apparatus similar tothat of the Prussian philosopher, long before his time, although no accountof them is extant. But if even such had been made, they would not lessenin any degree the merit of Guerricke, since his experiment undoubtedlyoriginated with himself, and all knowledge of similar ones had been lost.

In this device we behold the same moving force, and the same mecha-nism for applying it, as were subsequently adopted in steam-engines, whichat first were little more than copies of this : for example, had a loadedpump-rod been suspended to the rope instead of the scale and weights,the apparatus would have differed from Newcomen’s engine only in themode of exciting the atmospheric pressure. To Guerricke, therefore, isdue the credit of having not on ly pointed out the po wer which alone gaveefficiency to the first steam-machines, but also of devising the most effec-

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No. 191. Guerricke. A. D. 1654.