192 FRAGMENTS OF 



diant heat, which far transcends the light in energy. This 

 condition of things applies to all bodies capable of being 

 raised to a white heat, either in the solid or the molten 

 condition. It would doubtless also apply to the luminous 

 fogs formed by the condensation of incandescent vapors. 

 In such cases when the curve representing the radiant en 

 ergy of the body is constructed, the obscure radiation tow 

 ers upward like a mountain, the luminous radiation resem 

 bling a mere spur at its base. From the very brightness 

 of the light of some of the fixed stars we may infer the 

 intensity of the dark radiation, which is the precursor and 

 inseparable associate of their luminous rays. 



We thus find the luminous radiation appearing when 

 the radiant body has attained a certain temperature ; or, 

 in other words, when the vibrating atoms of the body have 

 attained a certain width of sw r ing. In solid and molten 

 bodies a certain amplitude cannot be surpassed without 

 the introduction of periods of vibration, which provoke 

 the sense of vision. How are we to figure this ? If per 

 mitted to speculate, we might ask, Are not these more 

 rapid vibrations the progeny of the slower ? Is it not really 

 the mutual action of the atoms, when they swing through 

 very wide spaces, and thus encroach upon each other, that 

 causes them to tremble in quicker periods ? If so, what 

 ever be the agency by which the large swinging space is 

 obtained, we shall have light-giving vibrations associated 

 \vitli it. It matters not whether the large amplitudes be 

 produced by the strokes of a hammer, or by the blows of 

 the molecules of a non-luminous gas, such as the air at some 

 height above a gas-flame ; or by the shock of the ether- 

 particles when transmitting radiant heat. The result in 

 all cases will be incandescence. Thus, the invisible waves 

 of our filtered electric beam may be regarded as generating 

 synchronous vibrations among the atoms of the platinum 

 on which they impinge ; but once these vibrations have at- 



