202 THE CHEMISTRY OF THE SUN. [CHAP. 



coronal atmosphere and in course of destruction as their vapour- 

 densities carry them down ; and their absorption will not only be 

 small in consequence of the reduced pressure of that region, but 

 what absorption there is will probably be limited wholly or in 

 great part to the invisible violet end of the spectrum in the case 

 of such bodies as the pure gases and their combinations and 

 chlorine (see I. ante). 



The spectroscopic evidence as to what may be called the plasticity 

 of the molecules of the metalloids, including of course oxygen and 

 nitrogen, but excluding hydrogen, is so overwhelming, that even the 

 absorption of iodine, although generally it is transparent to violet 

 light, may (as I have found in a repetition of Dr. Andre ws's 

 experiments on the dichroism of iodine, in which I observed the 

 spectrum) in part be driven into the violet end of the spectrum, for 

 iodine in a solution in water or alcohol at once gives up its ordinary 

 absorption properties and stops violet light. 1 



Should subsequent researches strengthen the probability of this 

 working hypothesis, it seems possible that iron meteorites will be 

 associated with the metallic stars and stony meteorites with 

 metalloidal and compound stars. Of the iron group of metals in the 

 sun, iron and nickel are those which exist in greatest quantity, as I 

 have determined from the number of lines reversed. Other striking 

 facts, such as the presence of hydrogen in meteorites, might also be 

 referred to. 



An interesting physical speculation connected with this working 

 hypothesis is the effect on the period of duration of a star's heat 

 which would be brought about by assuming that the original atoms 

 of which a star is composed are possessed with the increased 

 potential energy of combination which this hypothesis endows them 

 with. From the earliest phase of a star's life the dissipation of 

 energy would, as it were, bring into play a new supply of heat, and 

 so prolong the star's light. 



After this paper was communicated to the Eoyal Society I 

 sent a communication to the Paris Academy on the same subject, 

 and in a private letter to M. Dumas, the perpetual secretary, 



1 I have since obtained the same result by observing the absorption of iodine 

 vapour in a white-hot tube. 



