just as has been shown to exist in the case of the peripteral system, so that again we find the analogy holds. Thus, let us suppose a straight conductor in a uniform rectilinear magnetic field, the conductor and the lines of force being at right angles, and let the conductor be part of a completed circuit of zero resistance, carrying a current of some stated strength; then the conductor will experience a force at right angles to the direction of magnetic flux = F. Now let us apply a force F1 equal and opposite to F, acting from without on the conductor, so that the latter will be held stationary; we may regard this force as the analogue of the weight of an aerodone supported in an Eulerian fluid, the electric current representing the cyclic component of the peripteroid motion, and the magnetic flux the superposed translation, in accordance with the régime of §§ 80 and 122.
If we suppose now a resistance to be inserted in the electrical circuit, the current, and therefore the force F, will tend to fall off, but the applied force F1 continues, so that the conductor is set in motion in the magnetic field and is maintained in motion, the energy expended by the applied force F1 being accounted for as energy lost in the electrical circuit; this is in fact the principle of the generation of an electric current by means of a dynamo.
The motion of the conductor under the influence of the force F1 corresponds in our analogy to the descent of an aerodone in its gliding path, the gliding angle being represented by the velocity of the conductor divided by the velocity of the magnetic flux.
It is difficult to carry the present analogy much further without some stretching of the imagination or distortion of fact; even thus far there are many difficulties. For example, there is nothing in the hydrodynamic analogue of the electro-magnetic system depicted to give the conductor a sense of direction in the magnetic flux; its only knowledge of its motion through the supposed hydrodynamic stream is its relative motion, and as such it is difficult to see in what manner a conductor consisting
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