﻿Widening of Spectrum Line*. 283 



sented by e~ at sin bt, has been treated by Garbasso *". I 

 presume that the form quoted relates to positive values of t 

 and that for negative values of t it is to be replaced by 

 zero. But I am not able to confirm Garbasso's formula f. 



As regards the fifth cause of (additional) widening 

 enumerated at the beginning of this paper, the case is 

 somewhat similar to that of the fourth. It must certainly 

 operate, and yet it does not appear to be important in 

 practice. In such rather rough observations as I have made, 

 it seems to make no great difference whether two surfaces of 

 a Bunsen soda flame (front and back) are in action or only 

 one. If the supply of soda to each be insufficient to cause 

 dilatation, the multiplication of flames in line (3 or 4) has no 

 important effect either upon the brightness or the width of 

 the lines. Actual measures, in which no high accuracy is 

 needed, would here be of service. 



The observations referred to led me many years ago to 

 make a very rough comparison between the light actually 

 obtained from a nearly undilated soda line and that of the 

 corresponding part of the spectrum from a black body at the 

 same temperature as the flame. I quote it here rather as a 

 suggestion to be developed than as having much value in 

 itself. Doubtless, better data are now available. 



How does the intrinsic brightness of a just undilated soda 

 flame compare with the total brightness of a black body at 

 the temperature of the flame ? As a source of light Yiolle's 

 standard, viz., one sq. cm. of just melting platinum, is equal 

 to about 20 candles. The candle presents about 2 sq. cm. 

 of area, so that the radiating platinum is about 40 as 

 bright. Now platinum is not a black body and the Bunsen 

 flame is a good deal hotter than the melting metal. I esti- 

 mated (and perhaps under estimated) that a factor of 5 might 

 therefore be introduced, making the black body at flame 

 temperature 200 as bright as the candle. 



To compare with a candle a soda flame of which the D- 

 lines were just beginning to dilate, I reflected the former 

 nearly perpendicularly from a single glass surface. The 

 soda flame seemed about half as bright. At this rate the 



CD 



intrinsic brightness of the flame was *> X <p = ^ of that of 



the candle, and accordingly Jqooo °^ * nat °^ ^ e black 

 body. 



* Ami. der Physik, vol. xx. p. 848 (1906). 



t Possibly the sign of a is supposed to change when t passes through 

 zero. But even then what are perhaps misprints would need correction. 



