20 PROCEEDINGS OP THE AMERICAN ACADEMY 



Wendell, was Bliss & Creighton 1182; it is regulated to mean time, 

 and has been in frequent use at the Observatory. 



Arthur Searle. 



The instrument was the five-inch telescope formerly mounted in the 

 "West Dome. As it was not provided with any stand, and as economy 

 was an object kept strictly in view during the preparations for the 

 transit, the best plan for using this telescope seemed to be to lay it 

 horizontally upon a rough frame, at a height of three feet from the 

 ground, before the south entrance of the Observatory. A plane mir- 

 ror of unsilvered glass, formerly used in photographing the sun, was 

 placed upon the block of stone at the east side of the steps of the 

 entrance. This mirror was attached to the frame originally prepared 

 for it, which is provided with screws for moving it approximately in 

 altitude and in azimuth. The dimensions of the mirror are 7^ by 6 

 inches, so that the sunlight reflected from it at moderate hour angles 

 was thrown upon the whole surface of the object-glass before it. The 

 two surfaces of the mirror are inclined to each other, so that only one 

 image of the sun is seen. In order to keep this image of the sun in 

 the field, the services of an assistant were necessary. Unfortunately, 

 the assistant who had accustomed himself before the transit to the 

 management of the mirror, considering the morning too cloudy for 

 any observation, did not arrive at the Observatory in season to take 

 part in the observations at ingress. No other assistant having the 

 necessary skill was available, and an attempt made to use the tele- 

 scope at ingress was therefore unsuccessful. 



At egress, the mirror was very successfully managed so as to keep 

 the required part of the sun's limb in view, and Professor W. A. 

 Rogers kindly undertook to record the times at which the observer 

 gave his signals. The observation of the third contact was accordingly 

 a satisfiictory one. Nine seconds before the time recorded as that of 

 the contact, the sun's limb became noticeably darkened at the place 

 of egress, but the shade was lighter than the tint of the planet itself. 

 The shade gradually darkened as the planet advanced, and at the time 

 recorded as that of contact a darkness equal to that of the planet's 

 disk had reached the limb of the sun. This phenomenon could not 

 be distinguished from that of geometrical contact. If the limb of the 

 sun had been steadier, it is possible that such a distinction might have 

 been made. The image, in fact, was by no means bad, but there was 

 sufficient nndulation to make a very exact observation of geometrical 

 contact impossible. Thirteen seconds after the recorded time it had 



