the Viscosity and Temperature of Gases. 83 



slight variations in water-pressure. An inspection of this 

 arrangement will show that when the flask is exhausted and a 

 vacuum produced at Gr, the air will enter at A under the atmo- 

 spheric pressure, and will pass with constantly diminishing 

 pressure to G; so that at any intermediate point, as the junction 

 of the two tubes at B C, we shall have a pressure intermediate 

 between the two extremes. It will also be seen that the same 

 volume of air is successively transpired through A B and C D, 

 provided that there be no leak, which was carefully guarded 

 against by making all the joints about C, B, and E (which 

 were the only ones that affected the results) as tight as pos- 

 sible. By the two baths, we may have the gas transpired suc- 

 cessively through A B and C D either at the same or at differ- 

 ent temperatures. Now if we denote by V 1; 1^, \ 1} rji, &c. the 

 volume of gas transpired by A B, the radius and length of A B, 

 and the coefficient of viscosity of the air passing through it, 

 while V 2 &c. represent the same quantities for C D — also if 

 Pi, Pi, Pi represent the pressure of the gas at A, B, C, and D 

 respectively as obtained from the gauge and barometer-read- 

 ings, then we may write* 



y ^7rRfc p\-p\ ^ 



8^!^! 2p 



Y 2 - ***#* Pl-Pl (3) 



8?7 2 A 2 2p 



But if both baths are at the same temperature Vi==V a if h = t 2 , 

 and / >7 1 =77 2 , whence we may write 



Bfr pi-pi 



Also in general it will be seen from the nature of the apparatus 



th a t L^ = ^ , where S x and S 2 represent respectively 



1 + aOi l + ub 2 

 the temperatures at which V] and V 2 are transpired. Hence 



Vi _ R ft3 P\~P\ l + aS 2 m 



y 2 ~lWpl-pfl + a8i KJ 



From equation (5) it will be seen that, in order to deter- 

 mine with this apparatus the ratio ^ : tj 2 between the coeffi- 

 cients of viscosity in the two tubes when the temperatures of 

 these are o\ and S 2 respectively, we have only to know the ratio 



T? 4 A 



of the dimensions as expressed by -±J. 9 and to measure pi,jp s , 

 * Pogg\ Ann. toI. cxxvii. pp. 199, 353. 



G2 



