374 Mr. J. N. Lockyer's Spectroscopic Notes. No. III. [June 11, 



r Continuous absorption at the red end 



not reaching to the more refran- 



Fourth stage X , B /rri . , 



gible end. (This absorption may 



I break up into channelled spaces.) 

 Fifth stage Unique continuous absorption. 



9. I shall content myself in the present note by giving one or two 

 instances of the passnge of spectra from one stage to another, beginning 

 at the fifth stage. 



From 5 to 4. 



1. The absorption of the vapours of K in the red-hot tube, described 

 in another note, is at first continuous. As the action of the heat is con- 

 tinued, this continuous spectrum breaks in the middle ; one part of it 

 retreats to the blue, the other to the red. 



From 4 to 3. 



1. Faraday's researches on gold-leaf best illustrate this ; but I hold 

 that my explanation of them by masses of two degrees of complexity 

 only is sufficient without his conclusion (' Researches in Chemistry/ 

 p. 417), that they exist " of intermediate sizes or proportions." 



From 3 to 2. 



1. Sulphur-vapour first gives a continuous spectrum at the blue end ; 

 on heating, this breaks up into a channelled space-spectrum. 



2. The new spectra of K and JSTa (more particularly referred to in the 

 third note) make their appearance after the continuous absorption in the 

 blue and red vanishes. 



From 2 to 1. 



1. In many metalloids the spectra, without the jar, are channelled; on 

 throwing the jar into the circuit the line-spectrum is produced, while the 

 cooler exterior vapour gives a channelled absorption-spectrum. 



2. The new spectra of K and ISTa change into the line-spectrum (with 

 thick lines which thin subsequently) as the heat is continued. 



VII. " Spectroscopic Notes. No. III. On the Molecular Struc- 

 ture of Vapours in connexion with their Densities/' By J. 

 NORMAN LOCKYEH, F.R.S. Received May 26, 1874. 



1. I have recently attempted to bring the spectroscope to bear upon 

 the question whether vapours of elements below the highest tempera- 

 tures are truly homogeneous, and whether the vapours of different 

 chemical elements, at any one temperature, are all in a similar molecular 

 condition. In the present note, I beg to lay before the Eoyal Society the 

 preliminary results of my researches. 



