284 



G. F. Rodwell and H. M. Elder on [Jan. 30, 



this way the vertical currents in the solar atmosphere, both ascending 

 and descending, intense absorption in sun-spots, their association with 

 the facula3, and the apparently continuous spectrum of the corona and 

 its structure, find an easy solution. 



We are yet as far as ever from a demonstration of the cause of the 

 variation in the temperature of the sun ; but the excess of so-called 

 calcium with minimum sun-spots, and excess of so-called hydrogen 

 with maximum sun-spots follow naturally from the hypothesis, and 

 afford indications that the temperature of the hottest region in the 

 sun closely approximates to that of the reversing layer in stars of the 

 type of Sirius and a Lyrse. 



If it be conceded that the existence of these lines in the chromo- 

 sphere indicates the existence of basic molecules in the sun, it follows 

 that as these lines are also seen generally in the spectra of two different 

 metals in the electric arc, we must be dealing with the bases in the- 

 arc also. 



January 30, 1879. 



W. SPOTTISWOODE, M.A., D.C.L., President, in the Chair. 



The Presents received were laid on the table and thanks ordered for 

 them. 



The following Papers were read : — 



I. " On the Effect of Heat on the Di-iodide of Mercury, HgL.'~ 

 By G. F. Rodwell, Science Master, and H. M. Elder, a 

 Pupil, in Marlborough College. Communicated by Pro- 

 fessor Tyndall, F.R.S., Professor of Natural Philosophy in 

 the Royal Institution. Received January 9, 1879. 



In continuation of the experiments on the effects of heat on the 

 chloride, bromide, and iodide of silver, which one of us has previously 

 Lad the honour of communicating to the Society,* it was thought to 

 be advisable to search in some of the other metallic iodides for mole- 

 cular anomalies similar to those presented by the iodide of silver. 

 Among these no substance appeared more likely to possess such 

 anomalies than the di-iodide of mercury. This substance, as is well 

 known, is dimorphous. In the amorphous condition it presents the 

 appearance of a brilliant scarlet powder, which, if heated, fuses at 

 200° C, and volatilises just above the fusing point to a vapour more 



* "Proc. Eoy. Soc," vol. xxv, p. 2S0. 



