REPORT OF COMMITTEE ON OBSERVATORIES 9 1 



In the L,os Angeles region it soon became apparent that the height 

 of the fog at this season varies greatly on different days. One morn- 

 ing it will be lying almost in contact with the ground and not 

 advancing far from the sea. More frequently, however, the upper 

 level has an elevation of from 3,000 to 4,000 feet, only occasionally 

 exceeding the latter altitude. 



At Echo mountain the upper surface of the fog was sometimes 

 just below the Lowe Observatory. Whenever it was very near, the 

 seeing seemed to be unfavorably affected. When it was a thousand 

 feet or more below, no manifest influence was noted, either for good 

 or bad. 



The same characteristic was noted at Inspiration point. Here, 

 also, when the fog rose in the canyons to an elevation nearly equal to 

 that of my station, the seeing appeared to be unfavorably affected. 



Mount Wilson is somewhat protected from the direct drift of the 

 ocean fog by a spur of Mount Lowe, and during my stay at Mount 

 Wilson the fog did not at any time approach very near the summit. 

 At night currents of air were noticed descending the sides of the 

 mountain, and no doubt there were ascending currents during the 

 day. No ill effects from them were noticed. 



In the San Diego region, near the sea, fog is, according to the 

 United States Weather Bureau record, of daily occurrence during 

 most of the year. In San Diego, in summer, it is generally cloudy 

 at 5 a. m, and often so at 5 p. m. The middle portion of the day is 

 usually clear, or partially so. The record indicates less fog in winter 

 than in summer. The record does not contain any information re- 

 specting the altitude of the fogs. I was in San Diego county twenty- 

 five days, from May 19 to June 13, at a season when fog is said to 

 prevail to its greatest extent. On fifteen of these days mj^ observa- 

 tions showed that the summit of San Miguel, whose height is 2,600 

 feet, was either below or in fog or cloud a portion or all of the day. 

 On three days it was clear at the summit. On the remaining seven 

 days I was not where the peak could be observed. 



At Cuyamaca the ocean fog, blown in by strong westerly winds, 

 reached my level on two occasions, and I several times saw it to the 

 west, covering all the peaks in that direction lower than 3,500 feet. 



The prevalence of high fogs in these regions makes it evident that 

 an observatory should be placed at an elevation of more than 4,000 

 feet. 



Many of the days and nights at Mount Wilson are nearly wind- 

 less. Strong gales do sometimes blow ; some violent storms may be 



