50 ADDRESS TO THE BRITISH ASSOCIATION, 1881. 



Lockyer, by the application of the spectroscope, have 

 enabled us to study this region of the sun at all times. 



It is, moreover, obvious that the powerful engine 

 of investigation afforded us by the spectroscope is by 

 no means confined to the substances which form part 

 of our system. The incandescent body can thus be 

 examined, no matter how great its distance, so long 

 only as the light is strong enough. That this method 

 was theoretically applicable to the light of the stars was 

 indeed obvious, but the practical difficulties were very 

 great. Sirius, the brightest of all, is, in round numbers, 

 a hundred millions of millions of miles from us ; and, 

 though as big as sixty of our suns, his light when it 

 reaches us, after a journey of sixteen years, is at most 

 one two-thousand-millionth part as bright. Neverthe- 

 less as long ago as 1815 Fraunhofer recognised the 

 fixed lines in the light of four of the stars, and in 1863 

 Miller and Huggins in our own country, and Ruther- 

 ford in America, succeeded in determining the dark 

 lines in the spectrum of some of the brighter stars, thus 

 showing that these beautiful and mysterious lights con- 

 tain many of the material substances with which we 

 are familiar. In Aldebaran, for instance, we may infer 

 the presence of hydrogen, sodium, magnesium, iron, 

 calcium, tellurium, antimony, bismuth, and mercury; 

 some of which are not yet known to occur in the sun. 

 As might have been expected, the composition of the 

 stars is not uniform, and it would appear that they may 

 be arranged in a few well-marked classes, indicating 

 differences of temperature, or in other words, of age. 

 Some recent photographic spectra of stars obtained by 

 Huggins go very far to justify this view. 



