Days and weeks passed. When the opportunity presented, I consulted Dr. W. B. Chapman, the druggist and student of science, regarding the nature of light and earth, who in turn referred me to Prof. Daniel Vaughn. This learned man, in reply to my question concerning gravitation, declared that there was much that men wished to understand in regard to this mighty force, that might yet be explained, but which may never become known to mortal man. "The correlation of forces," said he, "was prominently introduced and considered by a painstaking scientific writer named Joule, in several papers that appeared between 1843 and 1850, and he was followed by others, who engaged themselves in experimenting and theorizing, and I may add that Joule was indeed preceded in such thought by Mayer. This department of scientific study just now appears of unusual interest to scientists, and your questions embrace problems connected with some phases of its phenomena. We believe that light, heat, and electricity are mutually convertible, in fact, the evidences recently opened up to us show—that such must be the case. These agencies or manifestations are now known to be so related that whenever one) disappears others spring into existence. Study the beautiful experiments and remarkable investigations of Sir William Thomson in these directions." "And what of gravitation?" I asked, observing that Prof. Vaughn neglected to include gravitation among his numerous enumerated forces, and recollecting that the force gravitation was more closely connected with my visitor's story than perhaps were any of the others, excepting the mysterious mid-earth illumination. "Of that force we are in greater ignorance than of the others," he replied. "It affects bodies terrestrial and celestial, "What of this ether?" I queried. "It is a necessity in science, but intangible, undemonstrated, unknown, and wholly theoretical. It is accepted as an existing fluid by scientists, because human theory can not conceive of a substance capable of, or explain how a substance can be capable of affecting a separate body unless there is an intermediate medium to convey force impressions. Hence to material substances Aristotle added (or at least made conspicuous) a speculative ether that, he assumed, pervades all space, and all material bodies as well, in order to account for the passage of heat and light to and from the sun, stars, and planets." "Explain further," I requested. "To conceive of such an entity we must imagine a material that is more evanescent than any known gas, even in its most diffused condition. It must combine the solidity of the most perfect conductor of heat (exceeding any known body in this respect to an infinite degree), with the transparency of an absolute vacuum. It must neither create friction by contact with any substance, nor possess attraction for matter; must "I can not conceive of such an entity," I replied. "No; neither can any man, for the theory is irrational, and can not be supported by comparison with laws known to man, but the conception is nevertheless a primary necessity in scientific study. Can man, by any rational theory, combine a vacuum and a substance, and create a result that is neither material nor vacuity, neither something nor nothing, and yet an intensified all; being more attenuated than the most perfect of known vacuums, and a conductor better than the densest metal? This we do when we attempt to describe the scientists’ all-pervading ether of space, and to account for its influence on matter. This hypothetical ether is, for want of a better theory of causes, as supreme in philosophy to-day as the alkahest of the talented old alchemist Van Helmont was in former times, a universal spirit that exists in conception; and yet does not exist in perception, and of which modern science knows as little as its speculative promulgator, Aristotle, did. We who pride ourselves on our exact science, smile at some of Aristotle's statements in other directions, for science has disproved them, and yet necessityI QUESTION SCIENTIFIC MEN.—ARISTOTLE'S ETHER.