gain in observational method, hut the design and 

 construction of Lord Rosse's instrument would 

 have precluded his use of the sensitive plate. The 

 types of telescopes adopted for our solar studies 

 have already been described. Let us now consider 

 the very different needs of stellar observations, 

 where the first requirement in many classes of 

 work is the collection of the greatest possible 

 amount of light. 



Kio. 38. Mirror Combinations in 6o-inch Reflector. 



Most of the astronomical telescopes in use are 

 refractors, consisting of a lens, through which the 

 rays from a star pass, to be united in an image at 

 the lower end of the telescope tube. A reflecting 

 telescope, on the other hand, consists of a silvered 

 concave mirror, lying at the lower end of a tube, 

 the upper end of which is open. The parallel 



