﻿[ 190 ] 



XXVI. On the Influence of Density and Temperature on the Spec- 

 tra of Incandescent Gases, By F. Zollner*. 



1. "17^ VERY gaseous body can, with respect to the rays emitted 

 -B-i from it, exist in two states essentially different from 

 each other. In the one the rays can be spread out into a so- 

 called discontinuous spectrum, with conspicuous maxima of bright- 

 ness; in the other, into a continuous spectrum. 



Both states are, analogously to the states of aggregation, 

 merely functions of the pressure and temperature. The researches 

 of Frankland, Wiillner, and others have proved that, in general, 

 the discontinuous-spectrum state passes into that of the continuous 

 spectrum by rise of temperature. But the transparency of the 

 incandescent body is common to both states ; and careful consi- 

 deration of this property, in connexion with those of the function 

 denoted by J in Kirchhoff s treatise " On the Ratio between the 

 Emissive and the Absorptive Power of Bodies for Heat and 

 Light "f, is, I believe, sufficient to explain the following phe- 

 nomena : — 



(1) The widening of the lines of discontinuous gas-spectra by 

 increase of pressure. 



(2) The change of a discontinuous spectrum into a continuous 

 one by increase of pressure. 



(3) The continuousness of the spectra of incandescent bodies 

 in the solid or liquid state of aggregation. 



(4) The dependence of the ratio between the intensities of two 

 lines of the spectrum on pressure. 



(5) The dependence of the different orders of spectra on tem- 

 perature. 



2. Let E A denote a homogeneous quantity of light, of the 

 wave-length X, emitted perpendicularly from the unit of surface 

 of an infinitely large plane, luminous layer of gas of the unit of 

 thickness ; and let A K denote the quantity of light of the same 

 wave-length absorbed by this layer, in terms of the quantity of 

 the incident light. If we imagine a series of any number m of 

 such layers, and calculate the quantity of light E Am emitted per- 

 pendicularly from a unit of surface of the layer of the thickness 

 m thus formed, we shall obtain for it the following expression :-— 



E ^-d-A.r Ea (1) 



■&\ 

 Let E Al and A A/ denote the corresponding magnitudes for a 

 wave-length X, very little different from the above, so that, on 



* Translated from a separate impression, communicated by the Author, 

 from the Berichte der K'on. Sachs. Gesellschaft der Wissenschaften, math.' 

 phys. Classe, Oct. 31, 1870, p. 233. 



t Poggendorff's Annalen, vol, cix. p, 291 et seqq. 



