BETWEEN ONK ATMOSPHERE AND HALF AN ATMOSPHERE OF PRESSURE. 



A MI. 



April 1 to 11, 1904 

 April 12 to 26, 1904 

 May 14 to 26, 1904 



9-5 

 11-3 

 13-5 



M.-an 



11-4 



1-00035 

 1-0001G 

 1-0001K 



1-00098 



In partial explanation of the high number which stands first, it should perhaps 

 he mentioned that the set of observations in question was incomplete. Owing to an 

 accident, it was impossible to return from the lower pressure to the higher pressure, 

 as had been intended. 



It may be well to repeat here that 



g _ pv at ^ atmosphere 

 pti at 1 atmosphere ' 



the temperature being constant and having the values recorded in each case. 



Although the accordance of results seems to surpass considerably anything attained 

 in observations below atmosphere at the time this work was undertaken, I must 

 confess that, except in the case of hydrogen, it is not so good as I had expected in 

 view of the design of the apparatus and of the care with which the observations were 

 made. I had supposed that an error of 3 parts in 100,000 (at the outside), corre- 

 sponding to I^Q C., was as much as was to be feared. As it is, I do not believe that 

 the discrepancies can be explained as due to errors of temperature, or of pressure, or 

 of volume so far as the readings are concerned. But it is possible that a variable 

 contact between mercury and glass in the lower chamljer of the first manometer may 

 have affected the volume in an uncertain manner, though care was taken to obviate 

 this as far as could l>e. It is to be remembered, however, that, except as to the 

 comparison of the two manometers, all sources of error enter independently in each 

 set of oKservations ; and that a mere repetition of the readings without a change in 

 the gas or in the pressure (from half atmosphere to one atmosphere, or rice verxA) 

 gave very much closer agreements. 



The values of B here discussed are the same as those given in the Preliminary 

 Notice,* except that no account was there taken of the small deviation in the ratio of 

 volumes from 2 : 1 in consequence of the yielding to pressure. If we measure p in 

 atmospheres and assume, as has been usually done, e.g., by REGNAULT and VAN DER 

 WAALS, that at small pressures the equation of an isothermal is 



* ' Roy. Soc. Proc.,' 73, p. 153, February, 1904. 



