“Passing onward to the gaseous state, still more of the evident characters of bodies are annihilated. The immense differences in their weights almost disappear; the remains of difference in color that were left, are lost. Transparency becomes universal, and they are all elastic. They now form but one set of substances, and the varieties of density, hardness, opacity, color, elasticity and form, which render the number of solids and fluids almost infinite, are now supplied by a few slight variations in weight, and some unimportant shades of color. “To those, therefore, who admit the radiant form of matter, no difficulty exists in the simplicity of the properties it possesses, but rather an argument in their favor. These persons show you a gradual resignation of properties in the matter we can appreciate as the matter ascends in the scale of forms, and they would be surprised if that effect were to cease at the gaseous state. They point out the greater exertions which nature makes at each step of the change, and think that, consistently, it ought to be greatest at the passage from the gaseous to the radiant form.”[24] [24] “Life and Letters of Faraday,” by Bence Jones. Vol. I, p. 307. This remarkable deliverance recalls what another great experimental philosopher, Count Rumford, deduced as by dint of mechanical motion he melted ice in a closed and insulated receiver. He inferred that the heat thus generated was not a material substance, as then generally supposed, but must be in essence motion, for only motion had brought it into existence. As we follow Faraday’s recital of the successive changes in properties which follow upon additions of heat, in other words, of mechanical motion, the inference is irresistible that properties consist in the distinct motions of masses of definite form and size, these very motions, perhaps, deciding both the form and size of each mass. CHAPTER XVI MEASUREMENT Methods beginning in rule-of-thumb proceed to the utmost refinement . . . The foot and cubit . . . The metric system . . . Refined measurement a means of discovery . . . The interferometer measures 1-5,000,000 inch . . . A light-wave as an unvarying unit of length.