60 SCIENTIFIC THOUGHT. 



clitions, able to produce these rotations. It was therefore 

 of interest to study the nature of rotational or whirling 

 motion, if such could exist in a perfect liquid, and to see 

 what would be likely to happen to these whirls. Though 

 it might be ditticult to understand how in a perfect liquid 

 rotation of any portion could be produced, calculation 

 misfht determine what would be the nature and fate of 

 such whirls, if they did exist. The problem was a 

 purely mathematical one. Can a rotational motion, a 

 whirl, exist in a perfect fluid, as defined by the mathe- 

 matical conception ? If it can, what are the properties of 

 such whirls, and what becomes of them ? Helmholtz 

 fiolved these questions in his now celebrated treatise, 

 showing that whirls (called by English waiters vortices) 

 can exist, but only under certain conditions, such as 

 can be experimentally represented by smoke-rings issuing 

 from an orifice ; that, if they existed in a perfect liquid, 

 they would be indestructible and would possess a motion 

 of their own, giving them a special individual character 

 as to permanence and movement. The treatise, like the 

 problem, was a purely mathematical one,^ and in the 

 mind of the celebrated author was probably connected 

 more with the problem of the formation of drops, and 

 with that of the friction or viscosity of fluids, which 

 he attacked subsequently, than with the nature of 

 matter. In this country vortex motion had already 

 been studied by natural philosophers with very different 

 ends in view. 



It was known that solid bodies which are in a rapid 



' It revealed incidentally the analogy of hydrodynamical and electrical 

 phenomena. 



