Ratio of the Specific Heats for Air and Steam, 



235 



Before proceeding to a discussion of the results obtained 

 for steam, the values of 7 obtained for air using the same 

 apparatus are given as an indication of its sensitiveness. 



Table III. 



Time of closing the 

 circuit in seconds (r). 



7- 



0-5S 

 1-21 

 2-00 



T397 

 1-392 

 1-392 



The value obtained with a platinum-blacked thermometer 

 was 1*374 ; the correction to be applied for radiation is 

 therefore *017, 



.-. 7 = 1-399. 



The striking agreement of this value with that obtained with 

 the large vessel demonstrates conclusively that it is possible 

 by the method here employed to work with quantities of gas 

 far smaller than has hitherto been supposed. 



8. Observations and Results. 



The observations were taken in a manner similar to that 

 adopted in the case of air ; it was, however, found incon- 

 venient to take all observations between exactly the same 

 pressure limits. The excess pressure was therefore adjusted 

 approximately to the same Aalue in each experiment, and. as 

 in the air-experiments, the sliding-contact was adjusted by 

 judgment nearly to the position where there would be no 

 current through the galvanometer at the instant when the 

 battery-circuit was closed ; from the initial and final tempe- 

 ratures and pressures a value of was calculated, which. 



7 

 as has been shown above, is proportional to the fall of tem- 

 perature for a constant excess pressure. The kicks of the 

 galvanometer-needle were recorded and a correction applied 

 7 -l 



to the value of 



obtained, in order to allow for the fad 



that the sliding-contact had not been exctcbly adjusted to the 

 correct position. 



In the first series of observations a kick of 1 scale-division 



