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Page 330 - ... of those fundamental modes, if some of the incident light is of one or other of their periods, or some of one and some of the other; so that the energy of the waves of those particular qualities of light is converted into thermal vibrations of the medium and dispersed in all directions, while light of all other qualities, even though very nearly agreeing with them, is transmitted with comparatively no loss. (5) That...
Page 329 - Miller, which showed it to be accurate to an astonishing degree of minuteness. (3) The fact that the yellow light given out when salt is thrown on burning spirit consists almost solely of the two nearly identical qualities which constitute that double bright line. (4) Observations made by Stokes himself, which showed the bright line D to be absent in a candle-flame when the wick was snuffed clean, so as not to project into the luminous envelope, and from an alcohol flame when the spirit was burned...
Page 352 - So that, generally, representing the interval between each soldier by an elastic cord, if the barrack and the eye approach each other by the motion of either, the cord will contract ; in the case of recession, the cord will stretch. Now let the barrack represent the hydrogen on the sun, perpetually paying out waves of light, and let the elastic cord represent one of these waves ; its length will be changed if the hydrogen and the eye approach each other by the motion of either. Particular wave-lengths...
Page 352 - ... towards you, now from you. In the first case the men will be paid out, so to speak, more rapidly. The motion of the barrack-gate towards you will plant each soldier nearer the preceding one than he would have been if the barrack had remained at rest. The soldiers will really be nearer together. In the second case, it is obvious that the interval will be greater, and the soldiers will really be further apart. So that, generally, representing the interval between each soldier by an elastic cord,...
Page 352 - You find that more soldiers pass you than change v before in the same time, and, reckoned in time, the interval between each soldier is less. You now move still slowly from the barrack, ie with the soldiers. You find that fewer soldiers now pass you, and that the interval between each is longer. Now suppose yourself at rest, and suppose the barrack to have a motion now towards you, now from you. In the first case the men will be payed out, so to speak, more rapidly. The motion of the barrack-gate...
Page 332 - Again, if the gaseous or vaporous substance gives out but few lines, then, although the light which emanates from it may be much less brilliant than that radiated by a solid or liquid, the light may be SO localized, and therefore intensified, in one case, and so spread out, and therefore diluted, in the other, that the bright lines from the feeble light source may in the spectroscope appear much brighter than the corresponding parts of the spectrum of the more lustrous solid body. Now here comes...
Page 330 - ... it has two fundamental notes or vibrations of approximately equal pitch ; and that the periods of these vibrations are precisely the periods of the two slightly different yellow lights constituting the double bright line D. (3) That when vapour of sodium is at a high enough temperature to become itself a source of light, each atom executes these two fundamental vibrations simultaneously ; and that therefore the light proceeding from it is of the two qualities constituting the double bright line...
Page 353 - Next fix your attention on the edge of the globe — the limb, in astronomical language ; here it is evident that an upward or downward movement is as powerless to alter the wave-length as a lateral movement was in the other case, but that, should any lateral or cyclonic movement occur here of sufficient velocity, it might be detected. So that we have the centre of the disc for studying upward and downward movements, and the limb for studying lateral or cyclonic movements, if they exist. If the hydrogen-lines...
Page 316 - ... different for a different form of the curve. May not the colours of the fixed stars be owing to a difference of this kind? white will acquire a tinge of yellow ; if the blue and green be successively stopped, this yellow will grow more and more ruddy, and pass through orange to scarlet and blood red. If, on the other hand, the red end of the spectrum be stopped, and more and more of the less refrangible portion thus successively abstracted from the beam, the white will pass first into pale, and...
Page 330 - ... other ; so that the energy of the waves of those particular qualities of light is converted into thermal vibrations of the medium, and dispersed in all directions, while light of all other qualities, even though very nearly agreeing with them, is transmitted with comparatively no loss. (5) That Fraunhofer's double dark line D of solar and stellar spectra is due to the presence of vapour of sodium in atmospheres surrounding the sun and those stars in whose spectra it had been observed. (6) That...