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Page 350 - 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 326 - ... 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...
Page 350 - 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 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...
Page 482 - The vast influence which the ocean must exert, as a moderator of climate, here suggests itself. The heat of summer is stored up in the ocean, and slowly given out during the winter. This is one cause of the absence of extremes in an island climate.
Page 326 - ... 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 351 - 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 328 - ... the spectroscope appear much brighter than the corresponding parts of the spectrum of the more lustrous solid body. Now here comes a very important point : supposing the continuous spectrum of a solid or liquid to be mixed with the discontinuous spectrum of a gas, we can, by increasing the number of prisms in a spectroscope, dilute the continuous spectrum of the solid or liquid body very much indeed, and the dispersion will not seemingly reduce the brilliancy of the lines given out by the gas...
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 450 - We have seen that the gaseous and liquid states are only distant stages of the same condition of matter, and are capable of passing into one another by a process of continuous change.
Page 326 - D, whether bright or dark, is due to vapour of sodium. (2) That the ultimate atom of sodium is susceptible of regular elastic vibrations, like those of a tuning-fork or of stringed musical instruments; that like an instrument with two strings tuned to approximate unison, or an approximately circular elastic...