The great Latter-day prophet is thus shown to be in harmony with the second fundamental law of science. It is not a valid objection to this conclusion to say that Joseph Smith did not use the accepted terms of science. Words stand only for ideas; the ideas are essential. The nomenclature of a science is often different in different lands, and is often changed as knowledge grows. It is hardly correct to say that he was in harmony with the law; the law as stated by the world of science was rather in harmony with him. Let it be observed that Joseph Smith enunciated the principle of the conservation of the energy, or intelligence as he called it, of the universe, in May, 1833, ten years before Dr. Joule published his famous papers on energy relations, and fifteen or twenty years before the doctrine was clearly understood and generally accepted by the learned of the world. Let it be also remembered that the unlearned boy from the backwoods of New York state, taught with the conviction of absolute certainty that the doctrine was true, for God had revealed it to him. If God did not reveal it to him, where did he learn it, and whence came the courage to teach it as an eternal truth? Chapter IV. THE UNIVERSAL ETHER. [Sidenote: The modern theory of light was established only about the year 1830.] The nature of light has been in every age a fascinating subject for study and reflection. Descartes, the French mathematician and philosopher, advanced the hypothesis that light consists of small particles emitted by luminous bodies, and that the sensation of light is produced by the impact of these particles upon the retina of the eye. Soon after this emission or corpuscular theory had been proposed, Hooke, an English investigator of great note, stated publicly that the phenomena of light, as he had observed them, led him to the belief that the nature of light could best be explained on the assumption that light was a kind of undulation or wave in some unknown medium, and that the sensation of light was. produced when these waves struck upon the retina of the eye. This new hypothesis, known as the theory of undulations, after the great Isaac Newton had declared himself in favor of the corpuscular theory, was finally adjudged by the majority of students to be erroneous.