1873.] Mr. J. N. Lockyer on Spectrum- Analysis. 285 



Experiment 5. — The selenium was also exposed to the spectrum of 

 the electric light in a darkened room. 



The effect was feeble ; but by using more battery-power in balancing, 

 it was possible to measure the swing of the spot of light when the 

 selenium was suddenly exposed to the action of the light of the spectrum. 



The maximum effect was obtained in, or just at the edge of the red, 

 the violet and blue rays producing scarcely any effect. 



Experiment 6. — The selenium was exposed to the full sunlight ; the 

 resistance fell enormously and instantaneously, and on balancing it was 

 found to be little more than half what it was in the darkness. 



The following were the general results of the experiments : — 



Results. — (1) That the resistance of selenium is largely affected by ex- 

 posure to light. 



(2) That this effect is not produced by the actinic rays, but is at a 

 maximum at, or just outside the red rays, at a place nearly coincident 

 with the locus of the maximum of the heat-rays. 



(3) That the effect of varying resistances is certainly not due to any 

 change of temperature in the bar of selenium. 



(4) That the effect produced on exposure to light is sensibly instanta- 

 neous, but that, on cutting off the light, the return to the normal re- 

 sistance is not so rapid. 



It would seem that there exists a power in rays nearly coincident with 

 the heat-rays of high intensity, of altering instantaneously and without 

 change of temperature the molecular condition of this particular element. 



II. " Researches in Spectrum- Analysis in connexion with the Spec- 

 trum of the Sun." — No. II. By J. Norman Lockyer, F.R.S. 

 Received March 14 ; 1873. 



(Abstract.) 



The observations in this paper are a continuation of those referred to in 

 the previous communication bearing the same title. They deal (1) with 

 the spectra of chemical compounds, and (2) with the spectra of mecha- 

 nical mixtures. 



I. Chemical Compounds. 



Several series of salts were observed ; these series may be divided into 

 two : — 1st, those in which the atomic weights varied in each series ; 2nd, 

 those in which the associated elements varied in each series. The 

 following salts were mapped : — 



Pb F 2 , Pb Cl 2 , Pb Br 2 , Pb I 2 ; Sr F 2 , Sr Cl 2 , Sr Br 2 , Sr I 2 ; Ba F a , 

 BaCl 2 , BaBr 2 , Bal a ; Mg F a , Mg Cl 3 , Mg Br 2 , Mgl 2 ; Na F, 

 NaCl, NaBr, Na I. 

 The conditions of the experiments are described. The same aluminium 

 cups, described in the first paper, were used ; and the poles were arranged 



