Another investigation that followed from this discovery had as its object the nature of the new forms of energy that evidently filled interstellar space. This was the province of the families devoted to astrophysics. They produced apparatus for isolating each type of energy which seemed to have full action only in a vacuum, and they experimented with it in an innumerable variety of ways so as to find out its characteristics. The force of gravitation had been familiar to them even in primitive ages, and had long been investigated so as to reveal many of the qualities of its action that were unperceived by ordinary senses. Electricity had been one of the commonest of their phenomena, and recently a vast unknown region had been opened up by them, lying between the verge of eye-awakening light and the verge of firla-awakening electricity which their machines had made plain even to untrained senses. For generations they had passed with ease in their inamars or spectroscopes beyond the bands of colour that affected their eye, and the unseen rays had yielded most of their secrets to them. In their lavolans or vacuum-energy mirrors they had traced the characteristics of the torrents of energy which tore away from the negative pole of their batteries. And now they had to face a new form of radiant energy, the product of these negative streams and of the irelium which they struck. Experimenting with it in their lavolans they found it different from its parent energy; by passing through the irelium it had grown indifferent to the power of magnetism. This peculiarity enabled them to investigate the inner nature of magnetism; for on the two sides of an irelium sheet they had the same electric rays acting differently towards a magnet; on the one side they could be deflected by it, on the other they went on their way as if it were not there. The difference was also used in producing a new kind of electric motor, governed by an irelium film which closed or opened a channel of magnetic influence. A third useful application of the discovery was a new irelium-covering for the head and the body, that milked the east wind of its deleterious qualities. And a fourth was an apparatus for finding by the aid of a magnet the stuff of irelium with greater certainty in their lava-wells.