the Viscosity of Liquids. 457 



For the small change of temperature assumed, 



fii—fi 2 Qi — 62 

 or 



n = A(e i -e)+ix l . 



Now, if dt be the time taken to traverse the distance dx, 

 the general equation of steady motion gives us 



dt = e£? 



k 



Let 0=f(a^ ) such that 



61 =f© and 2 =/(l). 

 Then the time taken for the whole descent 



I f ajdx = 'Bj the area of the temperature-curve, 

 Jo ^^ 



= 1 .0 mj if OT be the mean temperature ; 



But if the temperature had been uniformly 6 m throughout the 

 length ly the time r would have been 



where . ,„ ^ . 



/*«»= ^ 1 + A(6' 1 — V m ). 



Hence T = r. 



It therefore is only necessary to determine the mean tem- 

 perature during the interval, and even this is unnecessary if 

 our object is to compare two masses of mercury by their 

 speeds, if they are made to follow each other sufficiently 

 rapidly for the mean temperatures to remain constant in the 

 two cases. 



If a variation in temperature along the tube be suspected, 

 Phil. Mag. S. 5. Vol. 37. No. 228. May 1894. 2 I 



But 



