Report on the Solar Eclipse Expedition to Palgaon. 49 



by a partition into two square tubes of 7 X 7-inch section. In one 

 of these was placed the "Abney' : lens of 4 inches aperture and 

 5 feet 2 inches focal length, giving an image of the sun O57 inch in 

 diameter; in the other the photoheliograph objective (used in Transit 

 of Venus expedition), of 4 inches aperture and 5 feet focal length, 

 with a Dallmeyer secondary magnifier of 7|- inches focus placed 

 5 inches within the focus, the combination giving an image of the 

 sun 1^- inches in diameter. The camera was furnished with six 

 plate-holders, each taking two plates of 160 X 160 mm., as in use 

 for the astrographic chart, both plates being exposed by a quarter- 

 turn of one shutter. The camera was pointed to a 16-inch plane 

 mirror, made by Dr. Common, and mounted as a coelostat by Mr. 

 Hammersley after a design by Dr. Common, the sun's rays being 

 thus reflected into the telescope. 



The camera and ccelostat were not placed in a hut, but a screen of 

 bamboo matting was erected round the whole instrument, to protect 

 it from the wind, to which the ccelostat is particularly sensitive. 

 Another portion of bamboo screen was placed horizontally above the 

 camera, to protect the observer and the wooden body of the camera 

 from the direct rays of the sun. 



Mounting and Adjustment. The coelostat was placed on a masonry 

 pier level with the ground. As some trouble had previously been 

 experienced with the driving clock, owing to the heavy weight neces- 

 sary, care was taken on this occasion that it should be very rigidly 

 fixed in position. The method adopted was to screw the clock down 

 on to a stout wooden base-board, which in its turn was firmly 

 bolted to the masonry pier carrying the ccelostat, the driving cord 

 being led off horizontally under one pulley attached to the base- 

 board, and over another pulley hanging from the top of a strong 

 wooden trestle about 6 feet high. Railway fishplates were used as 

 weights. With this method no trouble at all was experienced, and 

 the clock-driving was irreproachable. 



In order to carry the camera, two parallel brick walls were built 

 on the west side of the ccelostat, and on the top of each of these a 

 4-feet length of heavy rail was placed, held in ordinary railway 

 chairs, lent for the purpose by the railway authorities at Pulgaon. 

 A wooden stop or button fixed on the under side of the camera rested 

 against the lower rail and prevented the camera from slipping down 

 towards the mirror. 



The angle at which the camera was set was so selected that the slide 

 end should be at a suitable height for working. It was found con- 

 venient to direct the camera towards a point about 30 below the 

 horizon, a little to the south of east. The focussing was done by 

 reflection, and calls for no special remark, the final adjust merit being 

 accomplished by using the ccelostat mirror. 



VOL. LXIV. E 



