Light Visible and Invisible

Abstract

THIS is an age of rapid growth of scientific knowledge when the theory of to-day becomes the established fact of to-morrow, and in no province have our ideas shown a more rapid advance than on the subject of radiations in the ether. First of all, the electromagnetic theory of Maxwell upheld that light was an electrical phenomenon, and this received its confirmation by the experimental genius of Hertz, and the subject of optics thus became attached to the domain of electricity. Later came the discovery, by Rontgen, of a kind of radiation entirely different from anything before known, and this was soon after followed by a discovery of a type of invisible radiation emitted by uranium and its salts, which apparently possess properties intermediate between ultra-violet Ifght and Rontgen-rays, but the cause of whose production? is at present one of the mysteries of science. Besides these, many-other types of radiation, either apparent or real, have-been noted, and the subject of transformation of radiations at the surface of bodies is now engaging the attention of many observers. The last few years has thus been an era of unexampled activity in the study of radiations, and there is considerable evidence that this activity will be productive of still further results in the near future.

Light Visible and Invisible.

By Prof. Silvanus P. Thompson, &c, Principal of, and Professor of Physics in, the City and Guilds Technical College, Finsbury. Pp. xii + 294. (London: Macmillan and Co., Ltd., 1897.)