VOL. XVI.] PHILOSOPHICAL TRANSACTIONS. 309 



great rains and hails. 3d. Tiie great quantity of nitrous and sulphureous ex- 

 halations in earthquakes. 4th. The sudden melting of snow in the high 

 mountains. 



The second part treats of the equilibrium of fluids. The 1st discourse de- 

 monstrates, from the principles of mechanics, how fluids counterpoise each 

 other's weight, and gives the rules for the doctrine of floating bodies. The 

 2d discourse shows the nature of the elasticity of air and flame, and how their 

 spring is counterpoised by weight. The 3d discourse treats of the equipollence 

 of a fluid body to a stroke or shock ; showing the rules for the force of jets 

 d'eau, from several heights of the reservatory, and different diameters of the 

 bore of the pipe ; giving also an account of the comparative force of wind and 

 water-mills with the manner of computing them. 



oj The third part treats of the measure of running and spouting waters. In 

 the 1st discourse, are produced several experiments to find the quantity of 

 water passing through a bore of an inch diameter, just under the surface of the 

 water. Notice is here also taken of the length of the pendulum vibrating se- 

 conds, in parts near the equinoctial, having been found at Cayenne a tenth, 

 and at the isle of Goree, near Cape Verde, an eighth of an inch shorter, than 

 at Paris ; the cause of which is stated to proceed from the diurnal motion of 

 the earth. 



The second discourse shows by experiment, that the quantity of water ex- 

 pended by a jet d'eau, of the same diameter of bore,' but at difl^erent heights 

 of the reservatory, are in a subduple proportion of these heights. The third 

 discourse shows, that the quantity evacuated by diff'erent bores, at the same 

 height of the reservatory, are as the squares of the diameters of the bores. 

 The fourth discourse shows, the manner of finding the quantity of water which 

 a river or an aqueduct furnishes, illustrated by the example of the Seine 

 at Paris. 



The fourth part treats of the height to which the water of fountains rises. 

 And its first discourse shows, that the jets d'eau never rise so high as their 

 reservatories, but always fall short, by spaces which are in duplicate proportion 

 of the heights they rise to ; which is proved by several experiments. The next 

 inquiry is, the best sort of ajutages or spouts for jets d'eau ; affirming from 

 experiment, that an even polished round hole in the end of the pipe, gives a 

 higher jet than either a cylindric or conical ajutage, of which yet the latter is 

 the better. A second discourse of this part treats on the amplitudes or distances 

 of oblique jets, according to the doctrine of Galileo and Torricelli, and con- 

 cludes with a geometrical way of finding the height of the reservatory by the 

 horizontal stream issuing out of a hole bored in the side of the pipe. 



