378 Mr. J. N. Lockyer's Spectroscopic Notes. No. IV. [June 11, 



11. It will be seen from the foregoing statement that if similar spectra 

 be taken as indicating similar molecular conditions, then the vapours, 

 the densities of which have been determined, have not been in the same 

 molecular condition among themselves. Thus the vapours of K, S, and 

 Cd, at the fourth stage of heat, gave us line, channelled-space, and con- 

 tinuous absorption in the blue respectively. This is also evidence that 

 each vapour is non-homogeneous for a considerable interval of time, the 

 interval being increased as the temperature is reduced. 



VIII. " Spectroscopic Notes. No. IV. On a new Class of Absorp- 

 tion Phenomena/' By J.NORMAN LOCKYER, F.R.S. Received 

 May 26, 1874. 



1. In the experiments on the absorption-spectrum of Na and K 

 vapour heated in a red-hot tube, to which further reference is made in 

 separate notes, I have observed phenomena quite new to me, some 

 rough drawings of which I lay herewith before the Royal Society. As 

 the phenomena are only momentary, I cannot answer for the final accu- 

 racy of the drawings, nor have I been able to represent the softness of 

 the gradations of shade. 



2. In the drawings, the red end of the spectrum is to the left ; the D 

 line common to them all is the image of a slit about half an inch long, 

 on which slit the light falls from an electric lamp, through the tube and 

 chamber in which the vapours are produced. The lower part of the 

 drawings would generally represent, therefore, the spectrum of the less 

 dense vapours were the vapours at rest. 



3. One of the phenomena referred to consists of what may be described 

 as a unilateral widening of the line D : the side absorption, however, is 

 much less dense than that of the line ; it is bounded by D on one side 

 and by a curved line on the other. Figs. 1, 2, and 3 will give an idea of 

 this appearance in three stages as it is frequently actually seen, i. e. as 

 the absorption travels up or down the line it widens as shown. 



Fig. 1. 



