Light energy : its physics, physiological action and therapeutic applications / by Margaret A. Cleaves.

  • Cleaves, Margaret Abigail, 1848-1917.
Date:
1904
Catalogue details

Licence: Public Domain Mark

Credit: Light energy : its physics, physiological action and therapeutic applications / by Margaret A. Cleaves. Source: Wellcome Collection.

Provider: This material has been provided by the Harvey Cushing/John Hay Whitney Medical Library at Yale University, through the Medical Heritage Library. The original may be consulted at the Harvey Cushing/John Hay Whitney Medical Library at Yale University.

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    against other molecules and a uniformity of pressure, i.e., of temperature would be established under ordinary pressures or even at moderate degrees of rarefaction. With the in- crease of rarefaction, however, the frequency of these inter- molecular shocks diminishes rapidly and in consequence a great number of the molecules, after having been heated by contact with the blackened sides of the palette, will strike against the cold glass. The effect of this will be to cool these molecules, that is, to diminish their velocity, and it will be this kind of molecules chiefly which will fall on the back of the disc and on the regions behind it. An excess of force equal and opposite to that on the glass acts against the front of the disc and accounts for the phenomenon exhibited by Crookes. Therefore, other things being equal a fly will rotate more rapidly in a small than a large bulb. Spectrum Analysis.—Spectrum analysis is a chemico- analytical method by means of which it is possible to deter- mine the constituents of a substance by observing the refrac- tion (dispersion) or the diffraction of light rays.1 It also offers an opportunity of investigating the molecular struc- ture of matter. When light rays are refracted the image produced is termed a spectrum. Rays of all refrangibility are emitted by white hot bodies and form what is termed a continuous spectrum, Plate 1. On the other hand, glowing gases of vapors emit rays of definite refrangibility. The spectrum of these is a discontinuous one consisting of bright lines which are characteristic of each substance. These characteristic lines serve for the identification of given sub- stances whether they exist singly or in connection with other bodies. In this way the constituents of the sun are known, as the solar spectrum with its many colors and shades of coloring is the written or pictured evidence of the nature of its molten matter. In the passage of rays from a white hot solid through a colored medium, some of them are retained and give an 'Ganot's Physics, 16th edition.