FIG. i. Mount Wilson from Pasadena 



TEN YEARS' WORK OF A MOUNTAIN 

 OBSERVATORY 



Ten years have elapsed since the inception of 

 the Mount Wilson Observatory, and the time is 

 opportune for a general survey of the work of the 

 past and the possibilities of the future. An exten- 

 sive equipment of buildings and instruments, 

 involving heavy initial cost and large annual ex- 

 penditure for operation and maintenance, has been 

 provided on a 6,ooo-foot mountain summit and in 

 the valley near its base. Activities of many 

 kinds, including the preparation of new plans of 

 research, the invention, design, and construction 

 of instruments, the building of a mountain road, 



(3) 



