'24 Prof. E. Copeland. 



sliding frame was drawn forward by a wire cord and weight, the rate 

 of motion being regulated by the speed at which the driving clock 

 " payed out " the cord. A tendency to advance by jerks was alto- 

 gether removed by thoroughly strengthening the clock seat-board 

 and its attachment to the fixed frame. The clock, kindly lent by 

 Lord McLaren, was made by Sir Howard Grubb. We utilised the 

 slide motion to obtain a chronographic record of the exposures. 

 Three pencils, in holders hinged to the standing part and moved 

 by strings, marked the time on a slip of paper pasted on the back of 

 the moveable frame. 



The distance of the plate-holder from the cell of the lens had 

 been found in Edinburgh to be 455*27 inches. This interval was 

 set off in India with light wooden rods, which were compared with 

 a Chesterman steel foot-rule. The photographic focus of the Dall- 

 meyer 4-inch had been found to agree exactly with the visual focus. 

 The instrument was focussed in India with the help of a focussing 

 glass, both in the day-time on an object at a distance of 440 yards, 

 and on stars at night, in the former case making allowance for the 

 divergence of the rays by means of the well-known formula for 

 conjugate foci. The two results were practically identical, but 

 differed considerably from the scale reading used at home, owing to 

 the shrinking of the wooden tube, in which the grain runs crosswise. 

 The tube of the Iceland spar camera, being made of well-seasoned 

 teak, was found unchanged in length, as proved by the linear 

 spectra of Sirius and 7 Argus. 



The greatest difficulty was experienced in filling the plate -holders 

 of the long-focus telescope. It was only after many hours spent in 

 paring and rasping the twisted frames that the plates were adjusted 

 and ready for exposure. Two plates were broken in the process. 



Our programme was as follows : Eight plates, 18 inches square, 

 to be exposed by Engineer McPherson standing in the dark room, 

 where he had control of the cord for opening the spring shutter, 

 were provided for the horizontal telescope, each carried in a separate 

 holder. The prism was to be pulled into position by our native 

 butler, Vardhya, at a signal from McPherson. 



Mr. Meehan, Assistant Engineer of the Public Works Department, 

 had kindly volunteered to work the Dallmeyer camera. He was pro- 

 vided with nine quarter plates, mounted in three long slides. The 

 shutter was of the ordinary pneumatic kind. 



I took charge of the ultra-violet prismatic camera, with six plates 

 in three reversible holders. I had also one plate (Cadett) in the 

 Grubb spectroscope, which was to be exposed by simply drawing 

 back the slide. Cadett plates were used for the horizontal telescope 

 and the 4-inch, while partly Lumiere and partly Cadett plates were 

 to be tried in the prismatic camera. 



