CHAPTER XXIII.
I QUESTION SCIENTIFIC MEN.—ARISTOTLE'S ETHER.
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,
