300 A. W. Witkowski on the 



In this manner we find, finally, 



M 1 = A 1 — m x ; M 2 = A 2 — m 2 ; 



these values substituted in (1) or (2) lead directly to the 

 coefficient ct Pt0 . 



§ 10. Corrections continued. — The first of the small capa- 

 cities denoted above by a and a- I determined by a simple 

 volumetric method, with the aid of the calibrated eudiometer 

 E and manometer M. It is superfluous to enter into par- 

 ticulars. I will mention only that the value of a has no 

 influence on the final result, provided we have exactly B = b ; 

 in general any small error in a influences the result quite 

 insignificantly. 



The second of these capacities, viz. c, is composed of two 

 parts : the capacity of the glass stem, and of the narrow 

 channels rst, together with the very small hole in the tighten- 

 ing lead plate. The capacity of the glass stem, reckoned 

 from the mark m, is obtained directly by weighing of mercury. 

 In order to find the rest (3 or 4 c. mm.) of the space <r, 

 I stopped the connexion between the glass stem and the 

 rest of the space a- by interposing another (not perforated) 

 lead plate and charged the channels several times with com- 

 pressed air, at 50 or 60 atmospheres. The quantity of the 

 collected gas having been measured with the aid of the 

 eudiometer, it is easy to calculate the capacity of the channels, 

 by applying Boyle's law, or better Amagat's results, for the 

 compressibility of air at ordinary temperatures. 



§ 11. Determination of Pressures. — The just mentioned 

 results of Amagat* render also possible the determination of 

 pressures. The pressures/), as already mentioned, I measured 

 by applying the i( constant volume " method, with variable 

 quantity of gas. This I will now explain. 



If a given quantity of air be compressed more and more, 

 by application of increasing pressure, then, as is well known, 

 the product of volume and corresponding pressure — far from 

 being constant, as it would be according to Boyle's law — 

 diminishes at first, until a certain pressure is reached, and 

 increases afterwards indefinitely (so far as known at present) . 



Let us denote by v the volume occupied under the pres- 

 sure of one atmosphere {=Pq), then we may express the law 

 of compressibility of air by the formula 



pv=e.p v Q , 



e denoting a coefficient variable with the pressure p. The 

 * Comptes Rend. 1884, p. 1154. 



