But such a hypothesis would be based upon the assumption that the sun was an electro-magnet, and then we should have to find out the cause of that fact also. Hence the hypothesis that the planets are magnets, because they are situated in the magnetic field of the sun, is not a satisfactory solution of the whole problem, as it fails to account for the fact that the sun is also an electro-magnet. We must therefore seek for another solution of the problem, which, while fulfilling all the Rules of Philosophy as laid down in [Art. 3], will also account for the sun being an electro-magnet, as well as every planet, satellite, meteor, or any other body that exists in space. If we can ascertain such a cause by philosophical reasoning, then we may say we have satisfactorily solved the problem as to the cause of all planetary and stellar bodies being electro-magnets.

If, at the same time, we can solve other outstanding problems by the solution thus offered, then such solution is more likely to be correct than if it simply solved the problem of solar magnetism. The only other solution that can possibly present itself to our minds, as to the cause of all magnetism in any planet, sun, or star, is the explanation which has already been given in [Art. 86] on electro-magnetism.

In that article we learned that magnetism was really due to the circular motion of an electric current; and that, whenever and wherever we had an electric current moving or revolving with a circular motion, there we should always have those conditions which would give rise to an electro-magnet. As long as the current continued to flow in its circular course, so long would there be those conditions which would give rise to permanent magnetism.

Now in the solar system we find that there are these magnets, which have been in existence for millions of years. We also learn from the electro-magnetic theory of light that Aether has an electro-magnetic basis, which gives rise to electro-magnetic waves when disturbed, or set in motion by any heated or luminous body. It can readily be seen, therefore, that we have only to set this electro-magnetic Aether in circular motion around any planet or sun, and we have at once a circular current of electricity flowing round that planet or sun, which would give rise to those conditions by which any body within its influence may be formed into a magnet.

Our hypothesis, therefore, to explain the reason why all the planets and the sun are magnets, is that the electro-magnetic Aether moves round the sun or planet or satellite as the case may be, thus giving rise to currents of electricity around the planet or sun, and so forming those conditions in the Aether by which the permanency of any planetary or stellar magnetism may be maintained and perpetuated.

In other words, to put it plainly and tersely, each aetherial atmosphere revolves round the planet, subject to certain limitations, in the same way that the aerial atmosphere turns round with the earth, as that planet revolves on its axis. At first sight, such an assumption may seem impossible, but a little careful consideration will show not only the possibility of such a cause, but will establish it, as the only reasonable and philosophical explanation for the phenomena we are seeking to explain, viz. the electro-magnetism of all celestial bodies.

There is nothing extravagant in this assumption, as we already have a similar illustration in the case of the atmosphere which goes round with the earth as it revolves on its axis. We have only to extend the same principle a little further, viz. to the aetherial atmosphere, and we at once get the true physical conception of the hypothesis suggested to explain the magnetism of all celestial bodies. We have already learned that Maxwell has proved that the equations for moving magnetic bodies are the same as those for stationary bodies, from which we came to the conclusion that the electric and magnetic field of any planet goes with that planet as it revolves on its axis in its journey round the sun.

I would like to ask the reader to try to conceive of any electric or magnetic field traversing space in association with any planet or sun which is revolving on its axis, while that electric or magnetic field does not revolve either partially or wholly with the revolving body. The field can only be stationary relatively to the planet or sun, as it revolves with the planet or sun on its axis.

There may be, as there doubtless are, conditions governing that revolution, as is the case with the atmosphere moving and revolving with the planet, but it is an absolute impossibility for Maxwell's equations relating to moving magnetic bodies to be carried to their logical conclusion, without affirming some such hypothesis as we have affirmed in relation to the cause of all solar magnetism.

Let me at once point out, this solution has already been offered by one whose name has been referred to several times. I refer to Professor Challis. Let us see what he has to say as to the cause of the earth's magnetism. In dealing with this subject, and writing in the Phil. Mag., 1872, par. 42, he states: “With respect to all magnetism which has a cosmical origin, the view I now take is that it is due to gyrations of the Aether, produced by the impulses which it receives from the motions of the constituent atoms of the bodies of the solar system. The gyrations may either be immediately generated by the rotations of the bodies about their axes, or directly result from disturbances of the Aether caused by their motions of translation. This impressed motion will be converted into circulatory or gyratory motion. Such circulatory motion will necessarily partake of the motion of translation of the bodies which generate them, so as to have always the same geometrical relation to these bodies provided their motion be uniform.“