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direct vision, which is more thoroughly established than this. It explains with the utmost simplicity, and without introducing any but the best-known properties of molecules, a great number of diverse phenomena seemingly incapable of explanation in any other way." Now, it is a great pity that these glad tidings did not reach Professor Clerk Maxwell before he was laid to rest in his early grave. They would certainly have been a great comfort to him, and possibly might have prolonged his life. For there is reason to suspect that in his latter days he arrived at conclusions respecting the kinetic theory of gases which bear a strange resemblance to my own. Being, not a scientific dogmatist, but an honest and candid investigator in search of truth, he came to see with ever-increasing clearness that the difficulties of his favorite theory beset not only its fundamental assumptions, but also their inevitable consequences, especially in their bearings upon the theory of heat. After the appearance of Watson's treatise already adverted to, on the 26th day of July, 1877, he published in "Nature" (vol. xvi, No. 404) a review of it, in which he considered the significance of Mr. Watson's propositions in connection with certain matters discussed on pages 97, 99, and 127 of my book. And thereupon he made this declaration ("Nature," vol. xvi, p. 245):

The clear way in which Mr. Watson has demonstrated these propositions leaves us no escape from the terrible generality of his results. Some of these, no doubt, are very satisfactory to us in our present state of opinion about the constitution of bodies, but there are others which are likely to startle us out of our complacency, and perhaps ultimately to drive us out of all the hypotheses in which hitherto we have found refuge into that state of conscious ignorance which is the prelude to every real advance in knowledge.

I hope, by-the-way, that this last remark of the great scientist will be pondered by those who complain that, after demolishing, as they imagine, all current physical theories, I leave them in the midst of ruins, and do not at once present them with a golden key for unlocking all the mysteries of the universe, or, like Puck, in "Midsummer-Night's Dream," "put a [theoretical] girdle round about the earth in forty minutes."

Before I leave this subject, I take the liberty of quoting another passage from the same article, which Professor Newcomb, if he knows anything about the discussions to which the kinetic theory of gases has given rise, will find instructive. Speaking of Boltzmann's attempt to reconcile the elasticity of atoms with their rigidity by increasing their co-efficients of elasticity ad infinitum, so as to make them practically rigid—a supposition also developed in an essay of Hugo Fritsch in Königsberg, entitled "Stoss zweier Massen unter der Voraussetzung ihrer Undurchdringlichkeit behandelt," which does not seem to have fallen under Professor Maxwell's notice (and, I may add, a supposition of which Professor Newcomb's "insuperable force" may