32 MOUNTAIN OBSERVATORIES IN AMERICA AND EUROPE. 



stars increased, their gain in brightness was proportionately more, so 

 that at 88 ° Z. D. stars were a full magnitude brighter on the Santis 

 than at sea-level. In all of Dr. Miiller's observations he noted the 

 steadiness of the air, as well as its transparency, and it follows from his 

 figures that the air was very quiet and the star-images free from 

 twinkling. 



It is difficult to make a comparison, but it would seem from an 

 examination of the figures that the steadiness of star-images on the 

 Santis during these observations was considerably greater than the 

 steadiness on Pike's Peak and in Colorado in the summer season, and 

 materially less than that at Mount Hamilton during the months June- 

 October. The comparison is, however, difficult to make with accuracy. 



Dr. Miiller's observations also related to a comparison of the solar 

 spectrum at high and low altitudes of the sun, and thus determined 

 the absorptive effect of a portion of the earth's atmosphere. It will 

 be observed that the programme of Dr. Mliller was concerned with 

 problems whose solution must depend upon the comparison of obser- 

 vations at high and low levels. The permanent meteorological 

 observatory afforded a convenient and comfortable station for his tem- 

 porary wants. The first cost of the observatory was about 60,000 

 francs ($12,000), and its annual budget is 6000 francs ($1200). 



THE METEOROLOGICAL OBSERVATORY ON THE SONNBLIOK (9843 FEET). 



From an account of the Sonnblick Observatory (8000 metres high) 

 in Himmel und Erde.^ vol. iv, a few statistics of interest to astrono- 

 mers are taken. The temperature-range (annual) is much less than at 

 sea-level, being only 14° C. (25°.2 F.). For 100 metres' increase in 

 altitude the temperature diminishes at the rate of -f^ of a degree C, 

 but the rate diminishes with increasing altitude. There must be a 

 point at which the summer and winter temperatures are alike — where 

 there is no annual range. From the data obtained from the Sonnblick 

 observations this height would be about 8800 metres (28,871 feet). 

 There are, on the average, two hundred and fifty days of the year 

 when the temperature is 0° C. or lower. 



The sunniest months yet experienced at the Sonnblick Observatory 

 during nearly seven years of observation are : 



February, 1890, 205 clear hours = 70 ^ of the maximum possible. 

 September, 1891, 203 " •' =58^ " 

 August, 1893,227 •' " =52^ " 

 July, 1893,204 " " =48^ " 



February, 1892, had only 48 hours of sunshine, and May, 1887, 

 only 73. 



