LECTURES. 217 



(114.) Elasticity of liquids. — The range of elasticity in these bodies 

 is exceedingly small when compared with that of gases, but the 

 elastic force is much greater. 



The diminution of bulk is found by experiment to be proportional 

 to the pressure. If B represent the bulk under a given pressure, P, 

 and other pressures be added in succession, then the corresponding 

 pressures and bulks will be as follows : 



P+p . . . B— 6 



P-f2p . . .' B— 2& 



P+3i9 . . . B— 3Z> 



P-j-wp . . . B — nh 



[t is evident that this law must have a limit ; otherwise the matter 

 may be annihilated by sufficient pressure. 



For a long time it was supposed that liquids were incompressible 

 and inelastic. Canton, in 1761, was the first who compressed water ; 

 since then the subject has been studied and extended by Perkins, 

 (Ersted and others. 



(115.) Perkins's apparatus ; — an iron bottle with a piston filled to 

 the neck ; pressure produced by sinking this into the deep sea. 



OErsted's apparatus exhibited. It consists principally of three parts : 

 1st. An exterior vessel which takes the place of the deep sea, and in 

 which the pressure is ^(produced by a screw and piston. 2d. Of an 

 inner vessel containing the liquid to be compressed called a Piezo- 

 meter, {ruzZin and ^srpou.) 3d. Of an inverted glass tube filled with 

 air, the diminution of which in bulk indicates the compressing force. 



Method of graduating the stem of the piezometer — each division 

 indicates the 2 millionths of the whole bulk. 



Self-registering piezometer for pressures whicli would break the 

 exterior glass vessel. 



Discussion as to the variation in the capacity of the piezometer. 

 According to Poisson it becomes smaller — according to QErsted, 

 larger. The opinion of the former is correct. 



The following is the compressibility of liquids, according to the 

 experiments of Colladon and Sturm of Geneva, expressed in millionths 

 of the primitive bulk, for an additional pressure of our atmosphere : 



Mercury, ...... 3.38 



Sulphuric acid, ..... 30.35 



Water not freed from air, . . . 47.85 

 Water freed from air, . . . . 49.65 



Alcohol, (1st atmos.) .... 94.95 



do., _ (5th do.) 91.89 



Sulphuric ether, (1st atmos.) . . . 131.35 

 do. do. (24tbdo.) . . . 120.45 

 The greater the density the greater the repulsive force. Change of 

 temperature affects the compressibility. 



(116.) The Elasticity of Solids. — This may be considered under 

 three heads : viz. , the elasticity of compression and dilatation^ of bend- 

 ing, and of torsion. 



Elasticity of Compression, &c. — In masses of solids, compressed on 



