248 NOTES. 



and writing &amp;lt; = ai^, where a is the velocity of the solid, we have, as in 



Arts. 86, 105, to write for , - a - -- , when the quantities to be 



clt doc 



differentiated are referred to axes fixed in the solid. On this supposition 

 the above formula? become 



a d\l/ ds 



and therefore 



i.e. V 2&amp;lt; is f the second order of small quantities. Hence to a first 

 approximation 



V 2 &amp;lt; = 0, 



i. e. the fluid moves sensibly as if it were incompressible. 



