An Introduction to the Study of Spectrum Analysis

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Longmans, Green, and Company, 1904 - Spectrum analysis - 325 pages
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Page 88 - ... by intervals relatively dark. The riddle of the nebulae was solved. The answer, which had come to us in the light itself, read: Not an aggregation of stars, but a luminous gas. Stars after the order of our own sun, and of the brighter stars, would give a different spectrum; the light of this nebula had clearly been emitted by a luminous gas. With an excess of caution, at the moment I did not venture to go further than to point out that we had here to do with bodies of an order quite different...
Page 96 - E. Wiedemann and others, there appears to be no certain direct relation between the luminous radiation as shown in the spectroscope and the temperature of the flame, or of the gaseous contents of the vacuum tube — that is, in the usual sense of the term as applied to the mean motion of all the molecules. In both cases, the vibratory motions within the molecules to which their luminosity is due are almost always much greater than would be produced by encounters of molecules having motions of translation...
Page 4 - When a ray of light passes from one medium to another, it is refracted so that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the velocities in the two media.
Page 88 - I looked into the spectroscope. No spectrum such as I expected! A single bright line only! At first I suspected some displacement of the prism, and that I was looking at a reflection of the illuminated slit from one of its faces. This thought was scarcely more than momentary; then the true interpretation flashed upon me. The light of the nebula was monochromatic, and so, unlike any other light I had as yet subjected to prismatic examination, could not be extended out to form a complete spectrum.
Page v - KirchhofFs original work on the solar spectrum and the interpretation of its lines. Since that time a great harvest has been gathered in the same field by many reapers. Spectroscopic astronomy has become a distinct and acknowledged branch of the science, possessing a large literature of its own, and observatories specially devoted to it. The more recent discovery of the gelatine dry plate has given a further great impetus to this modern side of astronomy and has opened a pathway into the unknown...
Page vi - What is heaven? A globe of dew, Filling in the morning new Some eyed flower whose young leaves waken On an unimagined world : — Constellated suns unshaken, Orbits measureless, are furled In that frail and fading sphere, With ten millions gathered there, To tremble, gleam, and disappear.
Page v - The more recent discovery of the gelatine dry plate has given a further great impetus to this modern side of astronomy and has opened a pathway into the unknown of which even an enthusiast thirty years ago would scarcely have dared to dream. In no science, perhaps, does the sober statement of the results which have been achieved appeal so strongly to the imagination and make so evident the almost boundless powers of the mind of man.
Page 86 - ... associated in my memory with the profound awe which I felt on looking for the first time at that which no eye of man had seen, and which even the scientific imagination could not foreshow. The attempt seemed almost hopeless. For not only are the nebulae very faintly luminous — as Marius put it, ' like a rush-light shining through a horn...
Page 90 - ... a tumultuous cloud Instinct with fire and nitre,' fell at once with the rise of the science of thermodynamics. In 1854 Helmholtz showed that the supposition of an original fiery condition of the nebulous stuff was unnecessary, since in the mutual gravitation of widely separated matter we have a store of potential energy sufficient to generate the high temperature of the sun and stars. We can scarcely go wrong in attributing the light of the nebulae to the conversion of the gravitational energy...
Page 96 - ... viva of the molecules may have no direct relation to the total radiation, which, on the other hand, is the sum of the radiation due to each luminous molecule. These phenomena have recently been discussed by Ebert from the standpoint of the electro-magnetic theory of light.' Very great caution is therefore called for when we attempt to reason by the aid of laboratory experiments to the temperature of the heavenly bodies from their radiation, especially on the reasonable assumption that in them...

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