Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/447



Eulerian theory of the inviscid fluid gives results that, it has already been remarked, bear but little resemblance to the behaviour of any actual liquid or gas. It is the more remarkable that these self-same results possess much that is in common with electrical phenomena. Thus the hydrodynamic plottings are true representations of the electrical and magnetic fields, and the theorem of energy and other Eulerian propositions in general apply.

The present analogy (for it is so far no more than an analogy) is one that has frequently attracted attention, and it is not without interest to follow the matter into the by-ways of hydrodynamic theory dealt with in the present work.

If we take the magnetic flux as the analogue of the flow (ψ function), then the electric current becomes a cyclic motion around the conductor. This point of analogy is emphasised by the need for a doubly or multiply connected region in both cases, in the case of the electric current for the completion of the circuit, and in the case of hydrodynamic theory in order that cyclic motion should become possible.

If the conductor be situated in a magnetic field, it will experience a force at right angles to the direction of the field