REPORT OF COMMITTEE ON OBSERVATORIES 1 7 



lated and reduced to routine in advance, the arguments in favor of 

 a subtropical station might be stronger than they are ; but we know 

 of no instance of the development of an important research outside 

 the temperate zones. One of the highest obligations of the pro- 

 posed observatory would be to follow up and take advantage of the 

 indications brought out by successive programs of observations. 

 Interpretation of results and choice of new and promising lines of 

 attack would probably be the yearly experience of such an observa- 

 tory, even though the main current of its work would consist of 

 comparative observations maintained through a long period. 



In order to secure the greatest freedom from atmospheric dis- 

 turbances and from the absorption of solar radiations by the atmos- 

 phere, one might suppose that an extremely high elevation, where 

 the observer would have below him as much of the atmosphere as 

 possible, should be chosen. How great this elevation ought to be is 

 involved in more than one consideration. The cost of maintenance 

 would alwa3 r s increase very rapidly with increasing altitude. This 

 becomes an important obstacle where a large observatory is in ques- 

 tion. At elevations much above 10,000 feet extremes of temperature 

 are likely to prevail, hurtful alike to the action of the instrument 

 and to the observer. The rarity of the atmosphere in producing 

 mental enfeeblement and prostration is a most serious drawback at 

 extremely great elevations. No doubt men accustomed to sea level 

 conditions can also live at altitudes exceeding 15,000 feet, if they 

 have nothing in particular to do ; but if they are to be called upon 

 for prolonged and intelligent exertion, the case is different. Further- 

 more, it is quite unlikely that the most favorable atmospheric con- 

 ditions are to be found above a certain moderate elevation. 



These considerations moved us to seek an elevation of from 4,000 

 to 6,000 feet for the main observatory, with the idea of selecting a 

 suitable auxiliary station at a much higher elevation for certain ob- 

 servations not requiring great steadiness of atmosphere, but needing 

 a transparent atmosphere. 



Our preliminary examination of climatic conditions seemed to 

 indicate that a suitable station could be found in California. The 

 steps which led to the provisional selection of Mount Wilson, a few 

 miles east of L,os Angeles, as the main station for the proposed solar 

 observatory are detailed in the section of this report appropriate to 

 that subject, and in the report of Mr. W. J. Hussey (Appendix A), 

 who was employed to make the requisite explorations and atmos- 



