The Radiometer and its Lessons

Abstract

As I now learn for the first time what are the grounds on which Prof G. C. Foster based his inculpation of me, I may ask for a very few last words. I fully admit that in giving a sketch of the history of the Radiometer, I intended to attribute to Mr. Crookes that he had in the first instance put a wrong interpretation upon his own results; because I believed that this was a simple fact, well known to everybody who had followed the history of the inquiry. And Prof. Carey Foster has not called in question the correctness of my statement of the general impression which prevailed among scientific men, alike when Mr. Crookes first exhibited his radiometer at the soirée of the Royal Society, and when its phenomena were discussed at the subsequent meeting. Having followed that discussion with the greatest interest, I cannot now recall one word that was not in harmony with the “direct impact” doctrine, or that suggested the idea of “heat reaction” through residual gas. If the question had been then asked, whether the rotation would continue to take place in an open vacuum (were such possible), or in a perfect vacuum,—so as to eliminate all “reaction”, through residual gas, between the vanes and the containing flask,—I believe that the general, if not the unanimous, verdict would have been in the affirmative. Certainly I heard nothing from Mr. Crookes on the other side, he having previously spoken of the dependence of the “Repulsion resulting from Radiation on the presence of residual gas as ‘impossible to conceive.’”