10 MOUNTAIN OBSERVATORIES IN AMERICA AND EUROPE. 



The observatory of Algiers probably lias fewer clouds tlian any 'i 

 other. In 1883 tlie sun was photographed there on 310 days.* 



Southern California, Egypt, Arabia, Madeira, Peru, parts of Austra- J 

 lia, etc., have excellent records in this regard ; not all of these regions * 

 are suitable for refined astronomical observations, however, as several 

 of them fail in respect of the most important condition, namely, 

 steadiness of the air. 



The advantage of a suitable station for astronomical work can be 

 strikingly illustrated by a comparison. Dr. Lewis Eutherfurd made 

 hundreds and hundreds of negatives of the moon, only a few of 

 which are of high excellence, the sole cause being the very unfavorable 

 situation of his observatory in the city of ISTew York. Dr. Henry 

 Draper, in 1877, reported that only three nights in two years gave 

 him good lunar photographs at his observatory at Hastings-on-the- 

 Hudson, where the steadiness of the air was not satisfactory. 



During August, 1888, photographs of the moon were made at Mt.j 

 Hamilton on the following dates. All the negatives were fairly good [ 

 and those marked with a star were very good ; with two stars, excellent :j 

 August 12*, 13*, 14**, 15** 16, 17, 18, 19 (no observations— Sunday),! 

 20, 21, 22, 23*, 24*, 25, 26*, 27*, 28*, 29 (no observations— the skyj 

 was clear), 80*, 31*. 



All the nights were clear — nearly all were good — and at least two] 

 of them were sujDcrb. 



Speaking broadly, and making every allowance for exceptions, it is] 

 true that, other things being equal, an astronomical station on an ex- 

 tended and elevated plain is preferable to one on a sharp peak. The! 

 conditions for level and tranquil arrangements of air-strata are morel 

 favorable in the former case. 



In any case, it is desirable that the surroundings of an astronomical 

 observatory should be uniform — homogeneous. The level verdant 

 plains of Lombardy, the small coral islets of the tropics of the Pacific,] 

 are examples. A level extensive plain of snow is not, in itself, objec- 

 tionable ; but such plains are ordinarily found in regions affected b] 

 other conditions which are distinctly unfavorable. 



High rocky peaks will usually have bad vision both night and day,' 

 owing to the heating of the rocks by day and to the air-currents (con- 

 trolled by the topography) by night. In regions (like California) 

 where the air is very dry, and where there is no great diurnal varia- 

 tion in temperature (as on the flanks of Mount Whitney, and elsewhere 

 in the Sierras), the conditions for good vision are very frequently 

 present. I should suppose, however, that they would vary very much 



* Publications of the Astronoviical Society of the Pacific, vol. iv, p. 268. 



