550 PHILOSOPHICAL TRANSACTIONS. PANNO 17^2, 



by the Calculus of those numbers, I have fitted to our president's theory of the 

 moon, the moon will be found to have arrived August the -^^ at 10*^ 57™ 36* 

 apparent time at London. But at Buenos Aires it was then computed but 

 7^ 5"" 38*; whence the difference of longitude, resulting from this observation, 

 is 3^ 52™ or 58^, more westerly than London. I have twice repeated the cal> 

 culation, to be sure to avoid error, and by comparing my chart of the variation 

 with the longitude thus found, 'it appears that in this case a ship at sea using 

 those tables, and that chart, would by an observation of this occultation have 

 fallen with greater exactness on the coast of America, than by any reckoning 

 can be pretended to be done. 



« 

 A Description of an Engine to raise Water by the Help of Quicksilver^ in- 

 vented by the late Mr. Joshua Haskins, and improved by J. T. Desaguliers, 

 LL.D. F.R.S. N°370, p. 5. 



Mr. Haskins finding that all hydraulic engines, working with pumps, lose a 

 great deal of water, always giving less than the number of strokes ought to 

 give according to the contents of the barrels ; and that when the pistons are 

 new leathered to prevent that loss, the friction is much increased, and the 

 engines are subject to jerks, which in great works often disorder them for 

 a great while, by breaking some of the parts ; contrived a new way of raising 

 water without any friction of solids; making use of quicksilver instead of 

 leather, to keep the air or water from slipping by the sides of the pistons in the 

 barrels where they work; hoping thus to prevent all the abovesaid inconveni- 

 encies, and also to have water engines less liable to be out of order than any 

 yet made. 



The first experiment he made with an engine that he set up at my house 

 about two years since, the description of which is as follows : 



In fig. 1, pi. 15, dddd represent a lignum vitae plug or piston, which Mr. 

 Haskins called a plunger, about 6 feet long, made heavy enough with lead at 

 top to sink into mercury, which is beforehand poured into the barrel d1 d2 up 

 to mm. The chain e1 e2, joined to the piston and the power that moves 

 it, being let down till the piston comes to d2, the mercury rises to the same 

 height in the barrel, and in the receiver r, which it fills, namely to nn, as 

 appears in the figure. Then drawing up the piston till its bottom is come to 

 mm, the mercury coming out of the receiver down to oo makes a vacuum, 

 and the weight of the atmosphere causes the water to rise up through the suck- 

 ing pipe A I a2, and valve v, into the receiver where the mercury was before. 

 On letting down the piston again, the mercury rises into the receiver, and 

 drives up the water through the elbow b, the forcing valve u, and so up the 



