348 Proceedings of the Royal Society of Edinburgh. [Sess. 
growing about the first direction at rate — Beoo(*) 3 . Thus, equating the 
total rate of growth of angular momentum about the first axis arising 
from these causes to the moment L of applied forces, we get 
Ao 1 — (B — C)a>2<o 3 = L. 
Similarly the other equations are obtained. 
The same kind of intuitive process is exemplified by the quaternion or 
vector treatment of motion ; but the discussion above seems to me to give a 
“ common sense ” view of the subject, unconnected with any formal process 
of analysis. It certainly enables a large number of problems of rotation — 
tops, gyrostats, etc. — to be solved with great ease and directness. 
(. Issued separately May 13, 1909.) 
