1865.] Badiatian. 709 



muscular system by what is called " reflex action." But should the 

 friction of the hard substance be sufficiently protracted and violent, or 

 if the substance itself be peculiarly susceptible (as in the case of 

 phosphorus), a third effect follows upon the production of heat, namely 

 luminosity, or the emission or radiation of light. This effect of the 

 motion of matter is conveyed to the optic nerve, and thence to the 

 brain, even where no atmosphere intervenes, and the medium of com- 

 munication is believed to be the " luminiferous sether" which is 

 supposed to pervade all space.* 



Thus it will be observed that the friction of some particular form 

 of matter may give rise to what are regarded as three distinct pheno- 

 mena — sound, heat, and light ; the first being sound, then, as the 

 vibration of its atoms become more rapid, heat, and finally, when the 

 temperature has been sufficiently raised, light is the result.f But this 

 may be merely an outline of the successive phenomena arising from 

 simple application of mechanical force to matter and the vibration of 

 its atoms. In the case of sound, the tone emitted may rise in intensity, 

 changing its quality as the vibrations become more rapid, and the 

 effect of a musical scale may be produced ; and in like manner the 

 rays of light emitted may, as the radiation becomes more rapid, not 

 only change their character to the appreciable sense, rising in the 

 scale of colour, to use a familiar expression, and perhaps producing 

 what to some organs of vision differing from ours, may form parts of 

 a chromatic or colour scale divisible into octaves, J but they may even 

 act as distinct forces, some with chemical effect, others with illuminat- 

 ing, and others again with thermic influences. Let us now, instead of 

 considering the phenomena attendant upon the heating of a substance 

 by friction, select an example, where the heat is the result of electri- 

 city, and we shall be enabled to obtain a very clear picture of the 

 effects just named. 



"Ifa current of electricity of gradually increasing strength be sent 

 through a wire of the refractory metal platinum, the wire first becomes 

 sensibly warm to the touch ; for a time its heat augments, still, how- 

 ever, remaining obscure ; at length we can no longer touch the metal 

 with impunity, and at a certain definite temperature it emits a feeble 

 red light. As the current augments in power, the light augments in 

 brilliancy, until finally the wire appears of a dazzling white. The 

 light which it now emits is similar to that of the sun."§ 



And if the light thus emitted be analyzed by means of a prism, as 

 it increases in brilliancy it is found " that when the platinum wire 

 first begins to glow the light emitted is a pure red. As the glow 

 augments the red becomes more brilliant, but at the same time orange 

 rays are added to the emission. Augmenting the temperature still 



* ' Radiation ' (Tyndall), p. 18. 



t In the case of glass or sealing-wax, we have sound, heat, and magnetism or 

 electricity. 



% See note on the " Probable Existence of tbe Repetition of Octaves in the Solar 

 Spectrum," by C. Hilton Fagge, M.D., 'Quarterly Journal of Science,' No. v., 

 p. 182, 



§ ' Radiation (Tyndall';, pp. 2, 3. 



