RADIATION. 303 



Thus the aui^mojitation of the electric current, which raises the wire from its 

 primitive dark coiulition to an intense white heat, exalts at the same time the 

 energy of the obscm'c radiation, until at the end it is fully 440 times what it was 

 at the beginning'. 



"What has been here proved true of the totality of the ultra-red rays is true for 

 each of them singly. Placing our linear thermo-electric pile in any part of the 

 ultra-red spectrum, it may be proved that a ray once emitted continues to be 

 emitted with increased energy as the temj)eratiu'e is augmented. The ])latinura 

 s])iral so often referred to being raised to whiteness by an electric current, a bril- 

 liant spectrum was formed from its light. A linear thermo-electric pile was 

 placed in the region of obscure rays beyond the red, and by diminishing the 

 current the spiral was reduced to a low temperature. It was then caused to pass 

 through various degrees of darkness and incandescence, with the following results: 



Appearauce of spiral. nergy o o - 

 ' ^ ^ scare rays. 



Dark 1 



Dark 6 



Faint red 10 



Dull red 13 



lied 18 



Appearance of spiral. "^sTuTe^ayf ' 



Full red 27 



Orange 60 



Yellow 93 



Full white 122 



Here, as in the former case, the dark and bn'ght radiation reached their maxi- 

 mum together ; as the one augmented the other augmented, until at last the 

 energy of the obscure rays of the particular reiVangibility here chosen became 

 122 tiii:ies what it was at first. To reach a white heat the wire has to pass 

 through all the stages of invisible radiation, and in its most brilliant condition it 

 still embraces, in an intensified form, the rays of all those stages. 



And thus it is with all other kinds of matter, as far as they have hitherto been 

 examined. Coke, whether brought to a white heat by the electric cuiTent, orl)y 

 the oxyhydrogen jet, poius out invisible rays with augmented energy as its light 

 is increased. The same is true of lime, bricks, and other substances. It is true 

 of all metals which are capable of being heated to incandescence. It also holds 

 good for phosphorus burning in oxygen. Every gush of dazzling light has 

 associated with it a gush of invisible radiant 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 Bolid or the molten condition. It would doubtless 

 also apply to the luminous fogs fonned by the condensation of incandescent 

 vapors. In such cases, when the curve representing the radiant energy of the 

 body is constructed, the obsciu'e radiation towers upwards like a mountain, the 

 buninous radiation resembling a mere spur at its base. 



What, then, is the real origin of the luminous radiation ? We find it appear- 

 ing when the radiating body has attained a certain temperature; or, in other 

 words, when tlie vibrating atoms of the body have attained a certain width of 

 swing. In solid and molten bodies a certain amplitude cannot be surpassed 

 without the introduction of periods of vibration, which provoke the sense of vision. 

 If permitted to speculate, one might ask, arc not these more rapid vibratitjns the 

 product 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, it matters not by what agency 

 the large swinging space is obtained ; we shall have light-giving vibrations 

 associated with it. It matters not whether the large amplitudes are 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 

 ])articles when transmitting radiant lieat. The result in all cases will bo incan- 

 descence. Thus the invisible waves of our liltercd electric beam, with which 



