156 CARNEGIE INSTITUTION OF WASHINGTON. 



for my experience on Mount Wilson. On certain occasions, it is 

 true, I had seen the solar image sharply defined on Mount Etna in the 

 very early morning hours. On Mount Hamilton, also, the solar 

 image is sometimes good ; but the testimony of those who have ob- 

 served the sun there was decidedly unfavorable. It was therefore 

 with, intense satisfaction that on each of the four days of my stay on 

 Mount Wilson I found the definition of the solar image almost per- 

 fect, to be rated at from 8 to 9 on a scale of 10. 



This visit was necessarily a hurried one, and it was evident that 

 before Mount Wilson could be determined upon as the best avail- 

 able site for an observatory, observations extending over a long 

 period of time would be necessary. As circumstances required that 

 my family should spend the winter of 1903- 1904 in Southern Cali- 

 fornia, I decided to take this opportunity to make a more complete 

 test of atmospheric conditions on Mount Wilson. Before arrange- 

 ments had been made for living upon the mountain, I made frequent 

 trips from Pasadena to Mount Wilson during the months of De- 

 cember, January, and February, observing the sun on each occasion 

 with a telescope of y/i inches aperture, and noting the prevailing 

 weather conditions. The extraordinary absence of wind, which had 

 seemed so characteristic a feature of the mountain during Professor 

 Hussey's visit, could not be said to continue throughout the winter 

 months. High gales sometimes occur at this season, and the average 

 wind velocity is greater than during the summer. Nevertheless, 

 the wind during the day was usually very light, and on many 

 occasions the quiet days of the previous June seemed to be almost 

 exactly duplicated, except that the temperature was lower. For weeks 

 together not a cloud would be seen in the sky, and the summer 

 serenity was in some measure retained until well into January. 

 Later it was broken by storms, but th^se practically ended with April. 



As the solar definition proved to be surprisingly good for this 

 season of the year, I was soon convinced that Mount Wilson oflFered 

 exceptional opportunities for both solar and stellar work and that 

 a systematic test of conditions should be inaugurated at the earliest 

 possible moment. Accordingly, I commenced on March i to render 

 habitable an old log cabin on the mountain that had been in a state 

 of partial ruin for many years. This cabin, known locally as the 

 "Casino," became our headquarters, where we have lived through- 

 out our work on Mount Wilson. Tests of the solar definition were 

 made as often as possible with the telescope already mentioned, 

 anrl on April 15 several meteorological instruments provided by the 



