Abstract
(From a German Correspondent.)
HERR NEESEN, assistant to Prof. Helmholtz, has recently published a memoir on the phenomena of attraction and repulsion by light and heat-rays, observed by Mr. Crookes. He states in it that he had already for two years observed such phenomena, which at first seemed to be a case of mechanical action of light-rays, i.e. of the effect of their impinging and rebounding on the surface of a mirror suspended by a cocoon-fibre. He now thinks, however, from the experiments he has made, that the effects of light and heat-rays in question are to be regarded as merely produced through air-currents arising from heating of the air in certain parts of the apparatus in which the movements of the mirror take place. Neesen first shows that in the phenomena observed such air-currents have, in fact, influence. He used for his experiments a rectangular case of sheet iron, in the upper cover of which was a peculiar arrangement for hanging a cocoon fibre. In the lower part of one of the sides of the case was a rectangular aperture closed by a plane parallel glass plate, and behind this plate was the suspended mirror. The air-currents above referred to arise not only from the fact that the air in contact with the glass plate through which the light must pass to reach the mirror, or the air in contact with the mirror, is heated. The air-particles also between glass plate and mirror are heated by conduction of the heat; and so, by their heating also, air-currents are produced which tend to turn the mirror.
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W. Science in Germany . Nature 13, 10 (1875). https://doi.org/10.1038/013010a0
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DOI: https://doi.org/10.1038/013010a0