6 Hartley & Ramagk — Wave-lengths of Principal Lines in Spectrum of Gallium, Sfc. 



special and peculiar treatment — we should expect to find that aluminous compounds, 

 from whatever source, and aluminium would furnish the gallium lines, which is 

 exactly in accordance with our experience. There can be no doubt, from the 

 relative intensities of the lines, from their wave-lengths, from the association of 

 gallium with aluminium and with iron, that the solar lines, 4172-211 and 4033-112, 

 have their origin from gallium contained in the sun, which is present in small 

 proportion when compared with iron, and that the solar spectrum, in so far as the 

 proportion of gallium to iron is concerned, maybe considered to be fairly imitated 

 by the arc spectrum of blast-furnace iron containing Yrlo^o-th of its weight of 

 gallium, since, if the more volatile metal were in any considerable proportion, the 

 gallium lines would be broader and overlap those of iron with wave-lengths, 

 4172-296 and 4033-224. 



This research brings to light the fact that, where coincidences are few in 

 number, the mere coincidences of lines in the spectra of terrestrial matter with 

 reversed lines in the solar spectrum is not equivalent to a proof of the existence 

 of the elements in the sun or other heavenly bodies, even when the most powerful 

 instruments are employed for resolving the lines. Professor Rowland's tables of 

 solar spectrum wave-lengths show not only how nearly lines of different elements 

 may coincide, but how there are some actual coincidences, as for instance of 

 nickel, with iron lines. Lines may also overlap. Generally speaking, two lines 

 of the same wave-length, belonging to different elements, differ in this respect, 

 that one is strong, and the other weak, or perhaps not so strong. 



Examples are familiar to us, and may be cited. For instance, two lines of 

 rubidium are very frequently obscured by two of iron ; the strong line of 

 rubidium corresponds with the weak line of iron, and vice versa.* If therefore the 

 two lines appear of the same intensity, we know that rubidium is present ; and 

 if the order of their intensity is the reverse of that of the iron lines, we know 

 then that the proportion of rubidium is larger than in the former case. Of 

 course, the presence of iron is determined by other lines than these two which 

 coincide with the rubidium lines. The greater mass of a substance may have the 

 effect of obscuring or extinguishing some of the lines in the spectrum of another 

 element less easily volatilised. On the other hand, the greater mass of a less 

 easily vapourised substance may also obscure the lines of one more volatile which 

 are in close proximity. 



In conclusion, we tender our sincere thanks to Dr. Adeney for the aid so 

 cordially given us in obtaining the photographs from which these measurements 

 have been made. 



* Wave-lengths of the rubidium lines, 4215-72 and 420r98. ; wave-lengths of the iron lines, 4216*28 

 and 4202-15. 



