324 PHILOSOPHICAL TRANSACTIONS. [aNNO I676. 



mortise aa, in which an iron nail, which passes through the handle of the 

 sucker, turns round when that sucker is raised or lowered. Near the body of 

 the pump is a copper vessel IHK, communicating with it by the tube G, and 

 having another tube KNL, which at N may be turned every way. 



To make this engine play, water is poured upon the chest to enter in at the 

 holes that are in the cover. This water is drawn into the body of the pump at 

 the hole F, when the sucker is raised ; and when the same is let down, the valve 

 of the hole F shuts, and forces the water through the hole M into the tube G, 

 of which the valve H being lifted up, the water enters into the pot, and filling 

 the- bottom, it enters through the hole K into the tube KNL, in such a man- 

 ner, that when the water is higher than the tube KNL, and the hole of the 

 tube G is shut by the valve H, the air inclosed in the vessel has no vent; and 

 when you continue to make the water enter into the vessel by the tube G, which 

 is much thicker than the aperture of the end L, at which it issues, it must 

 needs be, that the surplus of the water that enters into the vessel, and exceeds 

 that which at the same time issues through the small end of the jet, compresses 

 the air in the vessel : by which means, whilst the sucker is raised again to let 

 new water enter into the body of the pump, the air compressed in the vessel 

 drives the surplus of the water by the force of its spring, in the mean time that 

 a new depression of the sucker makes new water to enter, and causes also a new 

 compression of air. And thus the stream of the water, which issues by the 

 jet, is made to play continually. 



Extract of a Letter from S'lgnor Cassini to the Author of the Journal des Sfavans, 

 containing some Advertisements to Astronomers about the Configurations of the 

 Satellites of Jupiter, for the Years 1676 and 1677. N° 128, p. dSl. 



The configurations of Jupiter's satellites, which are observed this year 1676, 

 and which may be observed the next year, are of so great importance to the 

 verifying of their hypothesis, that Signor Cassini thought fit to advise astro- 

 nomers, not to let this occasion slip, which presents itself only twice in 12 

 years, of observing them with care and attention. For, by comparing the ob- 

 servations of this year with those of the next, they will find an apparent inver- 

 sion of the whole system of the satellites, which will happen towards the end 

 of March next, according to his particular hypothesis, which he proposes to 

 verify by comparing these observations with those of Galilasus, Marius, and 

 Hodierna, who undertook to give tables of their motions. 



Since the satellites have the centre of Jupiter for the centre of their particular 

 motions, and that the circles they describe are not directly opposite to the earth 

 nor the sun, there is always a part of each of those circles inferior to Jupiter, 



