Law of Molecular Force. 



171 



definite numerical values of T, and then by trial drawing the 

 isopiestic for P so that it cuts off equal areas. 



In the subjoined table I give the pressures of saturation as 

 found by the different experimenters and by Maxwell's prin- 

 ciple with the characteristic equation. Two series of deter- 

 minations by Regnault are given. Begnault is the only 

 observer who has reduced his air-manometer pressure to true 

 metres of mercury; but I have not thought it worth while to 

 apply any correction to the results of the other observers, in 

 view of the other larger sources of error that cannot be 

 allowed for. I have simply multiplied their pressures in 

 atmospheres by '76. The first row of numbers gives the 

 temperatures of observation and the second the corresponding 

 saturation pressures. 



Saturation Pressures of C0 2 . 



Tbilorier. 



Mitchell. 



Faraday. 



Eegnault, 

 I. 



30-90 

 5335 



Eegnault, 

 II. 



Andrews 

 (capill. 

 tubes). 



Maxwell's 

 principle 



and 

 equation. 



Temp. C... 

 Pressure... 



30-00 

 55-48 



30-00 

 54-72 





29-30 

 54-41 



28-3 

 53-5 



30 

 49 



Temp. C... 



Pressure... 





 27-36 





 27'36 





 29-26 



0-25 

 2717 



0-18 

 26-82 





 26-63 



0-21 

 26-2 



Temp. C... 

 Pressure... 







-26-10 

 13-53 



-25-8 

 12-9 



-25-5 

 12-9 





-25 50 

 13-35 



It will be seen that the equation gives results as good as 

 are to be looked for in view of the differences in the different 

 experimental determinations. The only number that is quite 

 out of harmony with all the experimental determinations 

 is 49, the pressure of saturation yielded by the equation 

 for 30°; but when we see that at 30 0, 9 Eegnault gets 53*35 

 in his first series, and that he finds a pressure greater by 

 1 metre, namely 54*41, in his second series for a temperature 

 l°-6 lower, which is equivalent to a difference of 2 metres out 

 of 50 in measurements made at the same temperature, we 

 cannot regard the difference of 49 from the experimental 

 numbers as serious, especially when we find Faraday's estimate 



