26 



PROCEEDINGS OF THE AMERICAN ACADEMY 



and fifth series. The first series was made with an apparatus totally 

 different from that afterwards used iii all details of disposition of parts 

 and of instruments used, except that the tube / of that series was the 

 same that was afterward cut into three pieces, of which two nearly equal 

 ones served as the capillaries in the fourth and fifth series. Observa- 

 tions with other tubes in the preliminary measurements, however, 

 checked satisfactorily with these. The instruments and arrangements 

 for measuring the pressures in the fourth series were wholly different 

 from those used in the fifth series. The results at 100° for the three 

 series are given in the following Table VII., in which the last two val- 

 ues are taken from the equation deduced for the respective series. 



TABLE VII. 



The quantity deduced as the result of each experiment of the 

 present investigation is a ratio between the coefficients of viscosity of 

 a gas at two different measured temperatures. As I have already 

 shown,* this ratio is expressible by the following equation : 



y = 



where 



coefficient of viscosity of the gas at f C. 



Z = " " '' " 0° C. 



i?2= radius, and X^ = length, of second capillary at <°. 



i?^ = radius, and Xi = length, of first " " 0°. 



jOj = pressure of gas at entrance to first capillary. 



p^ ^- " « exit from first capillary, which is the same 



as that at entrance to second. 

 p^ = pressure at exit from second capillary. 

 t = temperature of second capillary. 

 0° = " first " 



A = coefficient of linear expansion of the glass. 

 a = mean coefficient of expansion of the gas between 0° and t°, 

 and under the pressure p.y 



* See references at end of paper. 



