i PLEASANT WAYS IN SCIENCE. 



limits of the solid matter defined all these are questions 

 which must be answered before we can form a satisfactory 

 idea of the solar constitution ; yet they axe questions which 

 we have at present no means of answering." Again, we 

 require to know whether any process resembling combustion 

 can under any circumstances take place in the sun's globe. 

 If we could assume that some general resemblance exists 

 between the processes at work upon the sun and those we 

 are acquainted with, we might imagine that the various ele- 

 ments ordinarily exist in the sun's globe in the gaseous form 

 (chiefly) to certain levels, to others chiefly in the liquid 

 form, and to yet others chiefly in the solid form. But even 

 then that part of each element which is gaseous may exist 

 in two forms, having widely different spectra (in reality in 

 five, but I consider only the extreme forms). The light 

 of one part is capable of giving characteristic spectra of 

 lines or bands (which will be different according to pressure 

 and may appear either dark or bright) ; that of the other 

 is capable of giving a spectrum nearly or quite continuous. 



It will be seen that Dr. H. Draper's discovery supplies 

 an answer to one of the questions, or rather to one of the 

 sets of questions, thus indicated. I give his discovery as 

 far as possible in his own words. 



" Oxygen discloses itself" he says, " by bright lines or 

 bands in the solar spectrum, and does not give dark absorp- 

 tion-lines like the metals. We must therefore change our 

 theory of the solar spectrum, and no longer regard it merely 

 as a continuous spectrum with certain rays absorbed by a 

 layer of ignited metallic vapours, but as having also bright 

 lines and bands superposed on the background of continu- 

 ous spectrum. Such a conception not only opens the way 

 to the discovery of others of the non-metals, sulphur, phos- 

 phorus, selenium, chlorine, bromine, iodine, fluorine, carbon, 

 etc., but also may account for some of the so-called dark 

 lines, by regarding them as intervals between bright lines. 

 It must be distinctly understood that in speaking of the 

 solar spectrum here, I do not mean the spectrum of any 



