390 



Lord Kelvin 



[April 27, 



In both (a) and (/?), § 46, if we call 1 the velocity of the particle, 

 which is always the same, we have q 2 = sin 2 6, and the other com- 

 ponent of the energy is cos 2 0. In § 47 it is convenient to call 



the total energy 1 ; and thus 1 — q 2 is the total rotational energy, 

 which is constant throughout the flight. Hence, remembering that 

 the times of flight are all the same in case (a) and are proportional 



