46 REPORT OF THE SECRETARY. 



In view of the fact that the Observatory possessed a considerable 

 quantity of apparatus which could be usefully employed in the expe- 

 dition, and that the money could be chiefly allotted to the direct obser- 

 vations, the amount asked for was only $4:,000, and this, which was 

 granted bj'^ Congress, has been found, with strict econoni}-, to be 

 sufficient. 



The appropriation was made on February 9, and preparations were 

 immediately connnenced for a rehearsal of the actual observations, 

 which were to take place later. In doing this the Institution, which 

 had borrowed, through the great kindness of Prof. E. C. Pickering, 

 Director of the Harvard University Observatory, an achromatic lens of 

 12 inches aperture and 135 feet focus, installed this with numerous other 

 pieces of apparatus in the open space immediatel}' south and west of 

 the Astrophysical Observatory, and all the material of the future 

 camp Avas placed in position there and the observers accustomed to 

 such portions of the work as could be undertaken in rehearsal. 



The chief object of the expedition was intended to be the securing 

 of a number of photographs of the corona on different scales, and 

 especially on the unprecedentedh' large scale afliorded by the lunar 

 image of the 135-foot lens, which was about 15 inches in diameter. 

 This lens was, of course, placed so as to direct its beams horizontally, 

 the light l)eing fed into it b}' a "coelostat," the only considerable instru- 

 ment ordered specially for the expedition. 



A lens of 5 inches aperture and 38 feet focus, kindly lent by Pro- 

 fessor Young, of Princeton, was placed in position to point at the sun, 

 and the equatorial portion of the coelostat was made to carry a photo- 

 graphic telescope of 6 inches aperture and 7 feet focus for obtaining 

 photographs of the portion of the corona near the sun. In addition 

 to this, special preparation was made for a photographic search for 

 intramercurial planets, which will be described later. 



The question of the heat of the inner corona is an interesting one, 

 about which testimony differs, for although numerous attempts have 

 been made to measure it, they have been insufficient to give assurances 

 of an}^ positive result having been reached, particularly as some of them 

 have been in comparativeh^ inexperienced hands. The task of secur- 

 ing some authentic record of this with the bolometer the Secretary 

 assigned to Mr. C. G. Abbot, who has had long experience in the 

 use of the instrument and who was liberallv supplied with every 

 accessory that could be transported to the held, including the great 

 siderostat made b}' Grubb, which alone weighs many thousand pounds. 



It had at first been intended to establish the camp at Winton, North 

 Carolina, but after anxious consideration, Wadesboro, in the same 

 State, was sul)stituted, and Mr. Abbot, with some of his immediate 

 assistants, and all the heavier apparatus, left for that place on the 

 3d of Ma}-. Owing to the kindness of the United States Coast and 



