I. Experimental contributions to the theory of the radiometer.—Preliminary notice

Abstract

on some Chloro-brom-iodid of highly crystalline body (I speak of the iodide alone, not of the alloy) into a transparent, plastic, denser body. What the precise function of the molecular motion which disappears can be it is difficult to assume, since in this case it not only changes the state of the body, but approximates its molecules. Of the texture, specific gravity, <$fc. of the alloys.-It is noticeable that when the percentage of iodide of silver is small, the alloy is brittle while hot, and only slightly more tenacious than its constituents when cold (No. 1); as the percentage of iodide increases, the alloy becomes somewhat less brittle while hot, and considerably more tenacious, hard, and compact, than any of its constituents (Nos. 2 & 3) ; while when the percentage of iodide becomes considerable (Nos. 4 & 5), the mass becomes extremely plastic while hot, perhaps more so than the iodide itself, and very brittle when cold. The specific gravity is in all cases above the mean of that of the constituents; it may be because the intercrystalline spaces of the iodide are now filled with bromide and chloride. Thus, while the sp. gr. of Ag Cl is 5-505, of Ag Br 6*245, and of Ag I 5*675, that of the alloys is as follows :-No. 1, 6*152; No. 2, 6*1197; No. 3, 6*503 ; No. 4,5*9717; and No. 5, 5*907 : while the percentage of the bromide, which alone has a higher specific gravity than that of the alloys, in no case exceeds 42. In the accompanying curve table (p. 300) the expansion-curves of the iodide and bromide of silver have been added for comparison with those of the alloys; the curve of chloride of silver has been omitted, because it is [ almost precisely the same as that of the bromide. I have preferred to call these results " approximate " on account of certain experimental difficulties in the way of very precise determinations, which difficulties I at present see no way of avoiding.

Crookes's radiometers: a train of thought manifest

“…54 In Crookes's words, 'The radiometer is now so much occupying the attention of scientific men.' 55 Brock gives a detailed description of the theoretical arguments surrounding the radiometer. 56 In brief, it is this: the initial hypothesis that radiation pressure, a result of James Clerk Maxwell's recently published electromagnetic theory, 57 could explain the reaction of the blackened surfaces, was seen to be fallacious because the silvered surfaces should have been repulsed more strongly.…”