And still we see that under the _blue_ ray both vegetable and animal life manifest an inordinate development, while under the yellow ray it is proportionately arrested. How is it possible to account for this satisfactorily upon any other hypothesis than that both animal and vegetable life are differently modified electrico-magnetic phenomena, as yet unknown in their fundamental principles? Mr. Hunt finds that the undulatory theory does not account for the results of his experiments. Sir David Brewster, in his _Treatise on Optics_, showing that “the colors of vegetable life arise ... from a specific attraction which the particles of these bodies exercise over the differently-colored rays of light,” and that “it is by the light of the sun that the colored juices of plants are elaborated, that the colors of bodies are changed, etc....” remarks that it is not easy to allow “that such effects can be produced by the mere vibration of an ethereal medium.” And he is _forced_, he says, “by this class of facts, to reason as if light was _material_(?).” Professor Josiah P. Cooke, of Harvard University, says that he “cannot agree ... with those who regard the wave-theory of light as an established principle of science.”[253] Herschel’s doctrine, that the intensity of light, in effect of each undulation, “is inversely as the square of the distance from the luminous body,” if correct, damages a good deal if it does not kill the undulatory theory. That he is right, was proved repeatedly by experiments with photometers; and, though it begins to be much doubted, the undulatory theory is still alive. As General Pleasanton, of Philadelphia, has undertaken to combat this anti-Pythagorean hypothesis, and has devoted to it a whole volume, we cannot do any better than refer the reader to his recent work on the _Blue Ray_, etc. We leave the theory of Thomas Young, who, according to Tyndall, “placed on an immovable basis the undulatory theory of light,” to hold its own if it can, with the Philadelphia experimenter. Eliphas Levi, the modern magician, describes the astral light in the following sentence: “We have said that to acquire magical power, two things are necessary: to disengage the will from all servitude, and to exercise it in control.”