40 The Solar Eclipse of August last. [Jan., 



on August 4th, and up to the morning of the 7th they were occupied 

 in putting together the base and frame of the telescope, mounting the 

 bed-plate, the polar and declination axis and circles, the cradle 

 holding the telescope, fitting-in the tube and optical part, adjusting 

 the verniers and bringing the instrument into altitude and azimuth 

 adjustment. The whole of Friday, August 6th, there was a driving 

 rain, an east wind, and a dull murky atmosphere, foreboding the 

 worst results on the morrow — after having spent previous weeks in 

 preparation, and having travelled over a thousand miles, in the hope 

 of carrying back with them permanent photographic records of the 

 long-thought-of eclipse. 



As they retired to rest there appeared signs of the clouds 

 breaking. They had barely fallen asleep when the clerk, according 

 to previous arrangement, woke them with the agreeable news that 

 there were plenty of stars. They were soon dressed, and were 

 charmed by the sight cf a cloudless sky ; and Professor Coffin, Drs. 

 Gould and Mayer were up all night putting their own special 

 instruments in adjustment. When all was finished, the sun was 

 rising, and the air as pure and serene as one could wish. On 

 Saturday morning the chronograph was mounted, and electric 

 wires were led to the camera, to Professor Young's spectroscope, 

 and to the station of Dr. Gould outside the building. The two 

 threads of the reticule of the camera were placed one parallel and 

 the other at right angles to the celestial equator, and experiments 

 were now begun by Mr. Willard to ascertain the chemical focus. 

 This was obtained after the tube had been following the sun for an 

 hour or more, and after the focus was fixed the clockwork was kept 

 going, so that no change in focus should supervene from a change 

 in temperature in the lenses and tube. The clockwork adjustment 

 had been regulated with such accuracy that it drove the telescope so 

 that a star would remain closely bisected for twenty minutes. By 

 3 p.m. all was in readiness, and each one at his allotted post of duty, 

 ready for work. 



The image of the sun was 2 ■ 04 inches in diameter, and was 

 taken on a 4J x 5% inch plate. Mr. Zentmayer had so constructed 

 the camera eye-piece, that the image of a reticule of two spider- 

 threads at right angles to each other was formed on the plate with 

 the image of the sun, and these threads were so mounted that they 

 could be adjusted respectively parallel and at right angles to the 

 celestial equator, and thus fix on the photographs the positions of 

 the sun and moon, and give the position angles of points on the 

 surface and periphery of the sun. 



The tube carrying the camera lenses screwed into a plate in 

 which, immediately in front of the anterior lens, was a guide, in 

 which a thin plate having a horizontal slot of '0224 inch in width 

 was caused to descend by the action of a spring. This was used 



