90 



space, and measure the amount of scattering for 

 unit distance if a positive conclusion is reached. 

 This once accomplished, the determination of a 

 star's redness, after due consideration of the scat- 

 tering and absorbing effect of its own atmosphere, 

 will afford a measure of its distance, thus pro- 

 viding an invaluable means of sounding the great- 

 est depths of the universe. The closely entangled 

 question of the dependence of a star's redness upon 

 its physical condition, so important from the evo- 

 lutional standpoint, must also be cleared up. 

 Another capital problem is the actual extent of 

 Kapteyn's two star-streams, which the increased 

 light-gathering power of the loo-inch reflector 

 should help to reveal. Then there are such fun- 

 damental phenomena as the observed increase of 

 a star's speed with its age; the peculiar character- 

 istics of globular star-clusters, which contain so 

 many variable stars of short period; the significant 

 and intricate changes of variable stars of all classes; 

 the constitution and distribution of the nebulae. 

 But many pages would be needed to enumerate the 

 problems which press for solution, and from which 

 a selection must be made. 



In the laboratory the opportunities for useful 

 work are hardly less numerous. Tempted as we 

 often are toward the study of purely physical 

 questions, our chief effort must be devoted to the 

 interpretation of astronomical phenomena. Much 

 attention will be given to the investigation of the 

 Zeeman effect and the phenomena of radiation at 



