INSTRUMENTS AT BURNHAM. 485 



i 

 LOCATION OF THE INSTRUMENTS AT BURNHAM. 



The Altazimuth was 30 feet north and 65 feet east of the Transit ; the 

 6-inch Equatorial was 85 feet north and 37 feet east of the Transit ; the 

 Photoheliograph was 50 feet north and 25 feet west of the same instrument. 

 The instrument piers (of bricks laid in cement) rested on concrete founda- 

 tions, at depths 4 ft. 6 in. to 5 ft. 6 in. below the level of the ground. The 

 model, artificially representing the phenomena of the Transit of Venus, was 

 erected 400 feet from the Equatorial, on the bearing S. 60 E. The meridian 

 mark for the Transit was distant 6054 feet, and was found to be 4"'65 East 

 of South. 



THE TRANSIT CLOCK, 



originally made by Arnold for use at the Koyal Observatory, was placed in 

 the hands of Messrs. E. Dent and Co. in 1871, and was fitted with their 

 cylindrical zinc-and-steel-pendulum, the compensation of which was severely 

 tested at the Royal Observatory. - It was suspended on a solid tripod stand 

 of wood, which stood upon stakes driven deeply into the ground through 

 apertures in the floor of the transit observatory. 



The performance of the clock was, generally speaking, indifferent, though 

 it happened to be going pretty well about the time of the transit. Although 

 the tripod-legs were perfectly isolated from the floor of the hut when it was 

 put up, it was found on dismantling the hut (January 14) that there was contact 

 at one point between a leg of the tripod and the underneath part of the 

 flooring, which must have been caused by settlement of the hut ; and, if this 

 happened in the early part of our stay, it might account for the irregularity 

 of the rate. There was always much traffic about the clock, as the telegraph 

 instruments were inside the hut. [See Abstract of Tables IV. and V.] 



THE TRANSIT INSTRUMENT. 



The Transit instrument, its piers, the hanging level, and the wooden 

 observatory were in every respect similar to those used at Honolulu (pp. 9 

 et seq.) 



The Equatorial intervals of the ^vires were found by bringing each wire in 

 succession into coincidence with the image of the meridian mark by means 



