Isometrics of Liquid Matter. 339 



The literature of the subject, which I submitted at some 

 length elsewhere *, need not be repeated here. 



The work was suggested by Mr. Clarence King, and it 

 represents a stage of physical progress of an inquiry in which 

 we are conjointly interested. 



I. The Method of obtaining and of measuring High Pressures. 



1. Andrews's screw-compressor has an advantage, inasmuch 

 as the acting stress is brought to bear within the compass of 

 the barrel. In other arrangements, such, for instance, in 

 which a cylindrical plunger is forced home, stress must be 

 exerted on the bed-plate, or applied in a way tending to 

 flexure the plunger. The screw-compressor may therefore be 

 taken as the model of an apparatus of greater strength and 

 efficiency than was necessary in Andrews's f work. Hannay 

 and Hogarth % were the first to carry an improvement of the 

 screw into execution. They obtained pressures but little short 

 of 900 atmospheres, stating that their reasons for stopping 

 work at this datum were quite apart from the efficiency of 

 their apparatus. With the screw-compressor described below, 

 I reach and hold 2000 atmospheres with facility (§§ 17, 23). 

 It is so constructed that a large volume of liquid may be 

 operated on, admitting of a compression of five cubic inches. 

 Special provision has been made for the insulation of parts, 

 thus enabling the observer to apply the essential electric 

 methods § in studying his test samples. 



Particular notice should here be given of the remarkable 

 modification of Desgoffes's differential manometer, by which 

 Amagat || has measured over 3000 atmospheres ; but Prof. 

 TaitH recently described the " manometre a pistons libres " 

 in connexion with his own researches. The Bourdon gauge 

 has just been discussed by Prof. Grreenhill** and Mr. Worth- 

 ingtontf. The Bourdon gauge used below is of the kind 

 described by the former. 



* American Journal, [3] xxxix. pp. 478 to 481 (1890) j cf. ibid. [3] 

 xxxviii. p. 407 (1889). In these papers I endeavour to reach the iso- 

 metrics through the isothermals. 



t Andrews himself seems to have entertained this opinion. See Prof. 

 J. D. Everett's account in 'Nature/ xxxix. p. 556 (1889;. 



X Hannay and Hogarth, Chem. News, xli. p. 103 (1880). 



§ I have special reference to Prof. Tail's device. See Proc. Boy. Soc. 

 Edinb. xiii. p. 2 (1884-1885) ; Beiblatter, x. p. 149 (1886). 



|| Amagat, C. R. ciii. p. 429 (1886). 



If Tait, ' Challenger Reports' (1873-1876), Phvsics and Chemistry, II. : 

 see ' Nature/ xli. p. 361 (1890). 

 ** Greenhill, 'Nature/ xli. p. 517 (1890). 

 +t Worthington, 'Nature,' xli. p. 296 (1890). 



