Bjerknes s Experiments 315 3d
Fig. 5.

Very curious effects are also obtained with the arrangement shown in Fig. 6. Between the two drums there is introduced a body sustained by a float such as represented at a, Fig. 4. Various results may, then, be obtained according to the combinations adopted. Let us suppose that the phases are alike, and that the interposed body is heavier than water; in this case it is repelled as far as the circumference of the drums, at which point it stops. If the phases are different, the influenced body behaves in the opposite manner and stops at the center. If the body is lighter than water the effects are naturally changed. Placed between two like phases, it is attracted within a certain radius and repelled when it is placed further off; if the phases are unlike, it is always repelled. We may easily assure ourselves that these effects are analogous to those which are produced on bodies placed between the poles of wide and powerful magnets. It is useless to repeat that the analogies are always inverse.

Bjerknes s Experiments 315 3e
Fig. 6.

Mr. Bjerknes has carried the examination of these phenomena still further in studying experimentally the actions that occur in the depths of the liquid; and for this purpose he has made use of the arrangement shown in Fig. 7. By the side of the vibrating body there is placed a light body mounted on a very flexible spring. This assumes the motion of that portion of the fluid in which it is immersed, and, by the aid of a small pencil, its direction is inscribed upon a plate located above it. By placing this registering apparatus in different directions the entire liquid may be explored. We find by this means figures that are perfectly identical with magnetic phantoms. All the circumstances connected with these can be reproduced, the vibrating sphere giving the phantom of a magnet with its two poles. We may even exhibit the mutual action of two magnets. The figures show with remarkable distinctness - much more distinct, perhaps, than those that are obtained by true magnets.

Bjerknes s Experiments 315 3f
Fig. 7.

However, it must not be thought that these so interesting facts are the result of groping in the dark and the outcome of some fortunate experiment; for they have, on the contrary, been foreseen and predetermined. Mr. Bjerknes is especially a mathematician, and it was a study, through calculation, of the vibratory motion of a body or system of bodies in a medium that led him to the results that he afterwards materialized.

After the production, by Mr. Lejeune, of his solutions, Mr. Bjerknes in 1865 entered upon a complete study of the subject, and recognized the fact that the result of such motions was the production of regular mechanical actions. He calculated the directions of these, and, along about 1875, perceived the possibility of reproducing the effects of permanent magnetism. More recently, in 1879, he saw that magnetism by derivation might likewise be explained by those hypotheses, and figured by actions of this kind. It was not till then that he performed the experiments, and submitted a body to the results of calculation.

The same process has led him to the conclusion that the action of currents might be represented in the same manner; only, instead of bodies in vibration, it would require bodies in alternating rotation. The effects are much more difficult to ascertain, since it is necessary to employ viscid liquids.

Meanwhile, the experiments have been performed. Up to the present time attractions and repulsions have not been shown, and I do not know whether Mr. Bjerknes has obtained them. But, by the process pointed out, the lines of action (electric phantoms, if I may so express myself) have been traced, and they are very curious. By supposing the current perpendicular to the plate, and in the presence of the pole of a magnet, the influences produced around it are very well seen, and the figures are very striking, especially in the case of two currents. Mr. Bjerknes does not appear as yet to have obtained from these experiments all that he expects from them. And yet, such as they are, they have already led him to important conclusions. Thus, calculation, confirmed by application, has led him to renounce the formula proposed by Ampère and to adopt that of Regnard as modified by Clausius. Is he right? This is what more prolonged experimentation will allow to be seen.

These researches, however, are beset with difficulties of a special nature, and the use of viscid liquids is a subject for discussion. Mr. Bjerknes desired to employ them for reproducing the effects that he had obtained from water, but he found that the lines of force were no longer the same, and that the phenomena were modified. It is necessary, then, to hold as much as possible to liquids that are perfect. The experimenter is at present endeavoring to use these liquids by employing cylinders having a fluted surface; but it is clear that this, too, is not without its difficulties.

This series of experiments offers a rare example of the verification of algebraic calculation by direct demonstration. In general, we may employ geometry, which gives a graphic representation of calculation and furnishes a valuable control. Sometimes we have practical application, which is a very important verification in some respects, but only approximate in others. But it is rare that we employ, as Mr. Bjerknes has done, a material, direct, and immediate translation, which, while it brings the results into singular prominence, permits of comparing them with known facts and of generalizing the views upon which they are based.

Hypotheses as to the nature of electricity being as yet only tolerably well established, we should neglect nothing that may contribute to give them a solid basis. Assuming that electricity is a vibratory motion (and probably there is no doubt about it), yet the fact is not so well established with regard to it as it is to that of light. Every proof that comes to support this idea is welcome, and especially so when it is not derived from a kind of accident, but is furnished by a calculated and mathematical combination. Viewed from this double standpoint, the experiments of Mr. Bjerknes are very remarkable, and, I may add, they are very curious to behold, and I recommend all visitors to the Exhibition to examine them. - Frank Geraldy, in La Lumiere Electrique.