VOL. XXX.] PHILOSOPHICAL TRANSACTIONS. - 331 



petual motion, which seemed so plausible, and indeed so easily demonstrable 

 from an observation of the late Mr. Hawksbee, said to be founded on experi- 

 ment, that, though I am far from having any opinion of attempts of this nature, 

 yet I confess I could not see why it should not succeed. On trial indeed I found 

 myself disappointed. But as searches after things impossible in themselves are 

 frequently observed to produce other discoveries, unexpected by the inventor ; 

 so this proposal has given occasion not only to rectify some mistakes into which 

 we had been led, by that ingenious gentleman, but also to detect the real prin- 

 ciple, by which water is raised and suspended in capillary tubes, above the 

 level. 



My Friend's Proposal was as follows. — Let abc, fig. 2, pi. 8, be a capillary 

 siphon, composed of two legs ab, bc, unequal both in length and diameter ; 

 the longer and narrower leg ab having its orifice a immersed in water, the water 

 will rise above the level, till it fills the whole tube ab, and will then continue 

 suspended. If the wider and shorter leg bc, be in like manner immersed, the 

 water will only rise to some height as pc, less than the entire height of the 

 tube BC. 



This siphon being filled with water, and the orifice a sunk below the surface 

 of the water de, my friend reasons thus : Since the two columns of water ab 

 and FC, by the supposition, will be suspended by some power acting within the 

 tubes they are contained in, they cannot determine the water to move one way 

 or the other. But the column bf, having nothing to support it, must descend, 

 and cause the water to run out at c. Then the pressure of the atmosphere 

 driving the water upward through the orifice a, to supply the vacuity, which 

 would otherwise be left in the upper part of the tube bc, this must necessarily 

 produce a perpetual motion, since the water runs into the same vessel, out of which 

 it rises. But the fallacy of this reasoning appears on making the experiment. 



Exper. 1. — For the water, instead of running out at the orifice c, rises up- 

 ward towards f, and running all out of the leg bc, remains suspended in the 

 other leg to the height ab. 



Society, and for some time filled the office of one of their secretaries. He also succeeded Dr. 

 Tyson as president of the College of Physicians in Jan. 1750, but died the 22d of March following. 

 Dr. Jurin had great disputes with Michelotti, on the momentum of running water j also with Robins, 

 on distinct vision ; and with the partizans of Leibnitz, on the force of moving bodies A treatise of 

 his, on vision, is printed in Smith's Optics ; and he was concerned with Newton, in writing notes 

 for their improved edition of Varenius's Geography. His communications in the Philos. Trans, 

 extend from vol. 30 to vol. 66", inclusively. Dr. J. was among the earliest and most able advocates 

 for the inoculation of the small-pox, a practice at that time newly introduced into England, and 

 which had to struggle against the prejudices and opposition not of the vulgar only, but of a very 

 large proportion of medical practitioners in all parts of tlie kingdom. 



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