I may safely take it for granted after this, I presume, that, while Professor Newcomb may have a vocation for expounding and defending the kinetic theory of gases, he has no special call, as he supposes, to stand up for Clerk Maxwell and his opinions.
It is hardly necessary to say that Professor Newcomb does not honor my objections to the kinetic theory of gases with any notice or attempt at refutation. He observes that "an abstract of them is impossible," which is to be regretted, for, if he had undertaken to give us one, we should undoubtedly have learned some noteworthy things. The task of making such an abstract does not appear to be very difficult. What I insist on is, that every valid physical theory is essentially a simplification and not a complication, a reduction of the number of unrelated facts which it undertakes to account for, and not a mere substitution of many arbitrary assumptions of unknown and unverifiable facts for a few known facts—that is to say, speaking in the language of mathematics, that every true physical theory is in effect a reduction of the number of independent variables representing the phenomena to be explained. And I show that the kinetic theory of gases not only fails to satisfy this requirement, but is a complete reversal of a legitimate scientific procedure. This is the sense of the passage which Professor Newcomb parades before the unwary reader, whom he ought to have shocked still more with my horrible suggestion (which I now deliberately repeat) that a gas is in its nature a simpler thing than a solid, and that no attempt to account for its properties by taking those of a solid as a basis and making arbitrary additions to them is likely ever to succeed.
It is not a little instructive to note the character of sacredness ascribed by persons of Professor Newcomb's frame of mind to dominant physical theories, and the violence with which they repel every attempt to point out their defects. My reviewer in "The Critic" is almost beside himself after reading my "assault" on "that magnificent fabric of science, the undulatory theory of light and heat." Before he pelts me again with his missiles, he will do well to look and see who is standing at the place to which he directs them. There is at Harvard University a most learned and laborious scientist whose merits as an original investigator are at least equal, if not superior, to his inestimable services as an expounder of scientific truth, and the extent of whose attainments is no less conspicuous in his memoirs and books than the clearness of his intellect—Professor Josiah P. Cooke, Jr. In May, 1878, Professor Cooke published a lecture on the radiometer in this journal ("Popular Science Monthly"), in which he had occasion to speak of the undulatory theory of light and the luminiferous ether. And there (pages 11, 12) we find this language: