"The hypothesis that light is an electric phenomenon is thus made highly probable. To give a strict proof of this hypothesis would logically require experiments upon light itself. There is an obvious comparison between the experiments and the theory, in connection with which they were really undertaken. Since 1861, science has been in possession of a theory which Maxwell constructed upon Faraday's views, and which we therefore call the Faraday-Maxwell theory. This theory affirms the occurrence of the class of phenomena here discovered, just as positively as the remaining electric theories are compelled to deny it. From the outset, Maxwell's theory excelled all others in its elaboration and in the abundance of relations between the various phenomena which it included." How much Maxwell's work was appreciated across the channel, may be realized from what Poincaré said: "So sure did the results of his (Maxwell's) theory appear as worked out for the deepest problems, that a feeling of distrust and suspicion is likely to be mingled with our admiration for his magnificent work. It is only after prolonged study and at the cost of many efforts that this feeling is dissipated." Maxwell's explanation of electricity is that it is a strain or stress in the ether, that it is a condition or mode, and not a substance. One distinguished foreign contemporary who had read Maxwell's books with the greatest interest, declared that he could not be quite satisfied, since nowhere did he find what a charge of electricity is, though he seemed to find satisfactory information with regard to everything else. Maxwell realized, however, the limitations of his speculation very well, and hesitated, above all, to bind his mathematical conclusions to statements that might prove eventually only surmises founded on insufficient information from the standpoint of observation. Even when he gave his explanation, he did not insist on it as absolute, but, as pointed out by Poincaré, discussed it only as a possibility. The French scientist said: "Maxwell does not give a mechanical explanation of electricity and magnetism; he is only concerned to show that such an explanation is possible." Maxwell thoroughly believed in having a hobby as well as his regular work, and during the time while he was devoting himself to the mathematical explanation of electricity he turned for recreation to certain problems in physics, in physiology and psychology, relating to color. He worked almost as great a revolution in our knowledge of color-vision as in any other subject that he took up. Principal Garnett has condensed so well what Clerk Maxwell accomplished in the matter of color-vision, in his sketch of him in "The Heroes of Science,"[33] that I prefer to quote his explanation. He says: