THE SEARCH FOR AN IDEAL ASTRONOMICAL SITE. 



By Prof.- S. I. Bailey. 



The search for an ideal site for an Astronomical Observatory 

 has been long, and cannot yet be regarded as definitely com- 

 pleted. Indeed, the ideal locality probably does not exist. 

 Nevertheless, the most favourable site which our planet furnishes 

 must, sooner or later, be sought and found. The importance of 

 a suitable locality can hardly be over estimated. It is of equal, 

 if uol of greater, importance than increase in the size of telescopes. 

 In the past, Observatories have generally been i:)laced near large 

 towns, irrespective of the local climatic conditions, since the Gov- 

 ernments or LTniversities which founded them were so situated. 

 In the future, for their most defined results, astronomers must go 

 or send to localities where the best atmospheric conditions prevail. 

 The majority of astronomers, however, will have no need to thus 

 expatriate themselves, since, in many cases, photographs better 

 suited to their researches than any visual observations they them- 

 selves could make, could be taken and sent to them. It was 

 on this account some years ago that Professor E. C. Pickering, 

 Director of the Harvard Observatory, advanced the idea of an 

 International Observatory placed in the world's most favourable 

 region, whose chief duty it would be to. make photographs for 

 those astronomers of different nations, whose rank and abilities 

 entitled them to receive them. 



The first requisite for an astronomical station is a clear sky, 

 free from cloud, haze, smoke and dust. Since no locality is en- 

 tirely free from clouds, it is desirable that those clouds which do 

 occur should be distributed fairly evenly throughout the year, 

 rather than condensed into one decidedly " cloud}' season," a 

 condition which prevails in many countries. There are, more- 

 over, several other requirements, chief of which is steadiness of 

 the air. Visually, a steady atmosphere gives good " seeing," 

 and photographically fine definition and detail. With bad 

 atmospheric conditions a large telescope is often of no greater 

 value than a small one. Various other considerations enter into 

 the problem. An ideal locality would have freedom from strong 

 winds, especially at night, a small annual and diurnal range of 

 temperature, low humidity, a reasonable altitude, accessibility, 

 together with the necessities and some of the comforts of modern 

 life. For the present purpose also a station is desired sufficiently 

 far South of the Equator that the entire Southern sky may be 

 studied to the l)est advantage. 



In 1887 the Harvard Observatory received a fund, left by the 

 late Uriah A. Boyden, of Boston, for the establishment of an 

 observing station at an altitude where the atmospheric conditions 

 would be favourable to astronomical investigation. After numer- 

 ous trials of different locations in Colorado, California, Chili and 

 Peru, the proposed station was estafilished near Arequipa, Peru, 



