of the T rajectories of Shot. 



281 



whose abscissae are the corresponding velocities. Besides the immediate 

 purpose now in view, the same curve will be useful in exhibiting the 

 manner of change of the retardation ; since if y be the ordinate corre- 

 sponding to velocity v, the corresponding retardation will be 



d 2 180ff y 



W 7T V 



The primary use of these curves is that they enable us at a glance to 



