20 CARNEGIE INSTITUTION OF WASHINGTON. 



office hitherto, is now increasing, stimulated by two generations 

 of men unaccustomed to the practice of thrift and justified by 

 the widely prevalent but immoral theory that the Institution 

 may proceed "regardless of expense." 



One of the distinct, if relatively unimportant, misfortunes of 

 the world war was the delay in testing the capacities of the 100- 

 inch telescope named after Mr. John D. Hooker, 



?ele?cope" ^^ ^^^ Angeles, who made the initial contribu- 

 tion toward the construction of this instrument 

 thirteen years ago. It was substantially completed shortly 

 before the United States became a participant in the conflict. 

 About this time, also, the Director of the Observatory became 

 chairman of the National Research Council and he continued to 

 give all his time to this governmental organization until May of 

 this year. In the meantime, likewise, as already indicated, the 

 staff of the Observatory was preoccupied largely with military 

 rather than with astronomical affairs. Hence, opportunity has 

 only recently arrived for determination of the critical question 

 whether this ''largest telescope," which is 28 inches larger than 

 its largest predecessor, and 40 inches larger than the highly 

 successful 60-inch instrument completed by the Observatory 

 in 1908, would meet expectations in optical capacity and 

 practicability of operation. The construction of so large a 

 telescope has been regarded as one of the hazardous under- 

 takings of the Institution. Its optical perfection depends 

 on the stability of the glass used for its mirror; the stability 

 of the latter depends in turn on the rigidity of its mountings; 

 the requisites in both cases must take into account the elastic 

 mobility of materials and the disturbing effects on them of tem- 

 perature changes; and all these considerations must unite to 

 secure a combination which is manageable. The problems in 

 engineering thus presented have appealed very strongly to all 

 parties interested in such constructions, perhaps almost as 

 strongly as the astronomical possibilities anticipated from such 

 an extensive addition to visual apparatus. But the Director of 

 the Observatory now reports that the optical and the engineering 

 difficulties have been overcome and that the instrument under 



