46 PICKERING— INTERNATIONAL SOUTHERN TELESCOPE. [April iS 



during the remainder of the year. If we go further south, the pole 

 is higher, but the weather is more cloudy. Sir David Gill, Director 

 of the Cape Observatory, recommends Blomfontein. It is one of 

 the most promising locations. It is thirty degrees south of the 

 equator, and the pole is accordingly at that height. 



Form of Instrument. 



In the time of Franklin, mainly through the triumphs of Sir 

 William Herschel, the reflector was considered the best form of 

 telescope. This form has been frequently used ever since in Eng- 

 land, but until recently, it was seldom employed on the continent 

 or in this country. Dr. Henry Draper, nearly half a century ago. 

 recognizing the advantages of the reflector, constructed and used 

 with success one of the largest yet made in this country. One firm, 

 Alvan Clark & Sons, revolutionized public opinion regarding the 

 best form of telescope. The desire to possess the largest telescope 

 in the world has been a common one. There is perhaps no form of 

 memorial which has been more widely known and admired. Five 

 times the Clarks filled an order for the largest telescope in the world, 

 and, in each case except the first, the previous record was their own. 

 They accomplished this by making successively for the Mississippi, 

 Washington, Pulkowa, Lick, and Yerkes Observatories telescopes of 

 1 8, 26, 30, 36, and 40 inches aperture. In each case the telescope 

 was a complete success. They proved one of their principles, that 

 whenever they could see an error they could correct it. The limit 

 of size of telescopes of this form seems, however, to be nearly 

 reached. The cost is very great, and the engineering difficulties 

 become serious in the largest instruments. 



The genius of one man, the late James E. Keeler, Director of the 

 Lick Observatory, again revolutionized the views of astronomers 

 regarding the advantages of the reflector over the refractor. Having' 

 secured a three-foot reflector which previously had done but little 

 work, he obtained with it photographs of extraordinary perfection. 

 Similar results have since been obtained with the two-foot reflector 

 of the Yerkes Observatory. It has thus been shown that, in certain 

 departments of astronomy, especially in photographing faint stars 

 and nebulae, results could be obtained far beyond those which had 



4 



