,9o6T PICKERING— INTERNATIONAL SOUTHERN TELESCOPE. 45 



large cities, capitals of countries, or great universities. These are 

 centers of civilization, since the climate is temperate and frequent 

 rains promote agriculture, inland navigation, and the support of 

 large populations. The very conditions that have rendered man's 

 progress successful are those most unfavorable to good astronomical 

 work. Besides these, smoke, electric lights, and jars, all fatal to 

 the most careful study of the stars, accompany the growth of large 

 cities. If we divide the earth into cloudy and clear halves, nine 

 tenths of the observatories will lie in the cloudy regions. 



There are three extensive clear regions upon the earth. The 

 first and largest includes nearly all of the interior of northern Africa. 

 There is no large observatory in that region. The second is in 

 South Africa. The only large observatory there is in Capetown, 

 an exceptional cloudy part of that region. The third region is 

 the interior of Australia. The principal observatories are on the 

 coast, at Melbourne and Sydney. 



If we arrange observatories according to latitude, we find that 

 six sevenths of them are between latitudes +35° and -|- 60°, or the 

 latitudes of Spain and Scotland. A large part of the southern sky, 

 containing many of the most interesting objects, can never be seen 

 from the observatories of the United States or Europe. If we are 

 to erect the greatest telescope in the world it will have a much wider 

 field of usefulness if placed in the southern hemisphere, where com- 

 paratively neglected objects can be studied. 



A location should be selected at a considerable elevation, to avoid 

 the dust and haze of the lower atmosphere. These form the greatest 

 obstacles to the use of a large telescope, and their efifect is thus re- 

 duced to a minimum. In this respect no place is comparable with 

 South America, where one railway attains an elevation of 17,000 feet. 



Two locations suggest themselves, the west coast of South 

 America and South Africa. The Harvard College Observatory 

 after careful study, selected a point near Arequipa, Peru. For the 

 last seventeen years it has maintained a station there, at an elevation 

 of 8,000 feet. It is doubtful whether a better location can be found, 

 although it is open to two objections. It is so near the equator that 

 objects near the south pole are always low, and clouds are much 

 ]iiore frequent during the summer, from November to March, than 



