Total Solar Eclipse of 1901, May 17-18. 219 



canvas hut light-tight. The canvas was put on outside the frame- 

 work, and the roof was thatched with " alang-alang " on the top of the 

 canvas, to help to keep out rain and sun, and the thick paper was 

 tacked in position inside the framework. This was done in such 

 cunning fashion under Dr. Wallace's direction, that the hut was well 

 ventilated, and I doubt if so convenient and comfortable a dark 

 room has ever been constructed in the tropics. 



With reference to the dark room, I may add that a good supply of 

 ice for keeping the chemical and washing baths cool was obtained from 

 Padang, but this was only used for the plates that had to be preserved. 

 A great many of those taken in the process of adjusting the instru- 

 ments were entirely rotted when ice was not used, but as these were 

 only of passing value there was no object in preserving them. 



9. General Arrangement of the Instruments. 

 Inside the large hut three piers were built : 



(i.) One to carry the 4-prism spectroscope and the visual objective 

 grating ; top level and oriented north and south. 



(ii.) Another immediately to the west of it to carry the ccelostat ; top 

 level and oriented north and south. 



(iii.) A third, still more to the west, to carry the double tube 

 camera, the photographic objective-grating camera and other 

 apparatus, all inclined and pointing downwards towards the 

 cxelostat ; top inclined at an angle 22 with the horizon, and 

 in azimuth 70 west of south. 



The hut was set so that one diagonal of the base was parallel to 

 the length of the third pier, or in other words, to the double tube 

 camera ; the long sides of the hut thus lay nearly east and west. The 

 part of the roof over the N.E. corner was covered with the movable 

 corrugated iron, so as to admit the sunlight to the coalostat and 4-prism 

 spectroscope below. 



The two clocks for driving the ccelostat and the 4-prism spectroscope 

 were put on piers just outside the north side of the hut, and were 

 protected by sheets of corrugated iron leaning against that wall of the 

 hut. The weights for the ccelostat clock were hung over a pulley 

 attached to the bamboo framework that supported the thatch. 



The visual polariscopes were fitted to the framework of the hut up 

 in the N.E. corner. 



10. The Ccelostat. 



The 16-inch ccelostat, which was used by Professor Turner in India 

 in 1898, and in Algiers in 1900, had been specially provided, by the 

 care of Dr. Common, with an additional support to the mounting, 

 which made it quite stable and suitable for use on the equator. The 



