18 Messrs. Richardson, Nicol, and Parnell on the 
As it is difficult to draw tangents to a curve like that in 
fic. 5 very exactly, it was thought that a better test of the 
2) 2° >) 
SS) ° o © + 
Seale of y(=o—-,) in millimetres. 
accuracy with which the experimental results were expressed 
by the square-root law would be obtained by putting mn 
Scale of ¢ in minutes, 
