26 POPULAR SCIENCE MONTHLY. 



different parts of sun-spots and from other regions of the sun's surface. 

 Visual studies of the solar details under the best atmospheric condi- 

 tions, and direct photographs made in the ordinary way, will also be 

 essential. From such a mass of observations, if systematically made 

 and studied, a considerable increase in our knowledge of the solar con- 

 stitution might reasonably be expected to follow. 



It would be beyond the province of my immediate subject to discuss 

 the methods by which the study of the physical constitution of the 

 nebulas and stars may be expected to throw light on the past and future 

 of the sun. But I can not refrain from remarking that through recent 

 improvements in reflecting telescopes, and through the further im- 

 provements which are promised in the immediate future, a great ad- 

 vance in this department of astrophysical research may confidently be 

 expected. It thus appears that if the powerful instruments required 

 for these investigations can be provided, the opportunity should exist 

 during the next quarter of a century to make important additions to 

 our knowledge of the origin and development of the sun, and at the 

 same time to throw new light on the great problem of stellar evolution. 



