26 PLEASANT WA YS IN SCIENCE. 



Professor Langley, of the Alleghany Observatory, show that 

 we have not in the photosphere a definite bounding envelope 

 of the sun, but receive light from many different depths 

 below that spherical surface, 425,000 miles from the sun's 

 centre, which we call the photospheric level We receive 

 more light from the centre of the solar disc, I feel satisfied, 

 not solely because the absorptive layer through which we 

 there see the sun is shallower, but partly, and perhaps chiefly, 

 because we there receive light from some of the interior and 

 more intensely heated parts of the sun.* Should this prove 

 to be the case, it may be found possible to do what hereto- 

 fore astronomers have supposed to be impossible to ascer- 

 tain in some degree how far and in what way the constitution 

 of the sun varies below the photosphere, which, so fax as 

 ordinary telescopic observation is concerned, seems to present 

 a limit below which researches cannot be pursued. 



I hope we shall soon obtain news from Dr. Muggins's 

 Observatory that the oxygen lines have been photographed, 

 and possibly the bright lines of other elements recognized in 

 the solar spectrum. Mr. Lockyer also, we may hope, will 

 exercise that observing skill which enabled him early to 

 recognize the presence of bright hydrogen lines in the spec- 

 trum of portions of the sun's surface, to examine that 

 spectrum for other bright lines. 



I do not remember any time within the last twenty years 

 when the prospects of fresh solar discoveries seemed more 

 hopeful than they do at present The interest which has of 

 late years been drawn to the subject has had the effect of 



* It would be an interesting experiment, which I would specially 

 recommend to those who, like Dr. Draper, possess instrumental means 

 specially adapted to the inquiry, to ascertain what variations, if any, 

 occur in the solar spectrum when (i.) the central part of the disc alone, 

 and (ii.) the outer part alone, is allowed to transmit light to the spectro- 

 scope. The inquiry seems specially suited to the methods of spectral 

 photography pursued by Dr. Draper, and by Dr. Huggins, in this 

 country. Still, I believe interesting results can be obtained even with- 

 out these special appliances ; and I hope before long to employ my own 

 telescope in this department of research- 



