mountain observatories in america and europe. 65 



Echo Mountain, California (3500 feet). 



A private letter from Dr. Lewis Swift gives some statistics of the 

 weather at Echo Mountain which I quote : 



Between April 20 and December 1, 1894, there was only one rain of any 

 amount, and during that time the cloudy nights have averaged about three per 

 month. These statistics refer, of course, to the California dry season, the months 

 December to April being much less favorable. But after making all deductions 

 it is obvious that the number of clear nights at Echo Mountain is very much 

 greater than at any observing station east of the Sierra Nevada. Echo Mountain 

 (3500 feet) and Mt. Wilson (4700 feet) are reached by railway from Los Angeles and 

 Pasadena. Mt. Lowe (6000 feet) will soon be accessible in the same way. 



Chamberlin Observatory (5400 feet) near Denver, Colorado. 



Professor Howe, Director of the Observatory, in a letter of March 

 10, 1896, obligingly gives what data are available regarding the newly 

 established observatory. From August 24, 1895, to March 1, 1896 — 

 189 nights — must be deducted 65 nights of which no record was kept, 

 chiefly because the moon would interfere with comet-observations. 

 Of the 124 nights remaining 71 were utilized for work : 



I consider it safe to say that sixty per cent of the nights were clear. I 

 believe the half-j^ear from September to March is clearer than from March to 

 September.* 



My impression of the star-images is that there is more of dancing and shoot- 

 ing out of little arms than at lower altitudes, but less of blurring. On this ac- 

 count faint companions near bright stars are frequently hard to see. . . . 



I do not think there are more than twelve or fifteen first-class nights in a 

 year, but this is a matter of estimation rather than actual count. 



The transparency of the atmosphere about Denver is well known to 

 be remarkable, and is referred to by Professor Howe. 



The National Observatory of Mexico (Tacubaya) (about 



7500 feet). 



On March 5, 1896, I addressed a letter to Director Anguino asking 

 for data relating to the steadiness of star-images at Tacubaya, based on 

 experience. From his reply of April 9th the following paragraph is 

 quoted : 



In respect to the second question, the problem is complicated for us, not only 

 on account of the altitude, but because there is a local cause that perhaps has 

 more influence upon the photographic images — that is, the movement of the dust 

 constantly raised in the vaUey of Mexico. 



As yet we can say nothing that would be weU established, since it is a point 

 which I am yet studying, but we can advise you as we advance farther in the 

 study. 



* The clear half-year would be the period of unsteady images, so far as my per- 

 sonal observation in this region holds good. — Note by E. S. H. 



