Total Eclipse of the Sun, 1901, May 18. 



245 



Abney squares were printed on No. 6 by exposure to a standard 

 candle at a distance of 5 feet for 4 minutes with the Dallmeyer lens, 

 and 8 minutes with the Unar lens. It had been intended to print 

 squares on several plates, but the number of photographs to be dealt 

 with made it necessary to limit work as much as possible the night 

 before the eclipse when the photographic plates were taken from sealed 

 tins and put in their carriers, and after the eclipse it was necessary to 

 finish the developing as soon as possible. Of these photographs Nos. 5, 

 6, 7, 8 are the most successful. The extension shown with the Abney 

 lens reaches to 66' from the centre, and with the Unar lens to 77'. 



Venus and Mercury and a number of stars are shown on the Unar 

 plates. No. 5 is the best, and shows 7 stars of the Pleiades and 25 

 others of magnitudes ranging from 4 to 6, which have been identified. 

 Unfortunately, owing to the clouds, stars are not equally well shown 

 all over the plate, and S Tauri (4 m> 0) and Tauri (3 m> 9) are not shown ; 

 y Tauri (3 m> 9), which is near 6 Tauri, is, however, shown. 



It may be concluded that any object appreciably brighter than 4 m- 

 within the area covered by the plate (i.e. within 15 of the Sun) would 

 have been shown. 



III. The Spedroscopic Cameras. 



The two spectroscopes used by Captain Hills at the Indian Eclipse 

 of 1898 were kindly lent by him, and were used in Sumatra with the 

 following adjustments : 



Objective 



Collimator and ea- 

 rner* lenses 

 Prisms . 



Slit 



Priams at mnxi- 



mum deviation 



for 



Spectroscope No. 1. 



Cooke, achromatic, 4^-in. 



aperture, 6-ft. 2^-in. focus. 

 Single quartz lens, 2^-in. 



nperture, 30-in. focus. 

 Two dense flint prisms of 



<>0, 4i-in. base, 2Hn. 



height. 



H in. by 0'0015 in. 

 H (A 4340) 



Spectroscope No. 2. 



Single quartz lens, 5-in. 

 aperture, 4-ft. 7-in. focus. 



Single quartz lens, 3-in. 

 aperture, 33$ -in. focus. 



Four double quartz prisVns 

 of 60 (each prism being 

 composed of two half- 

 prisms of riglit- and left- 

 handed quartz), 3-in. 

 base, 2-in. height. 



2 in. by 0'0012 in. 



X3500. 



The width of the slit of the flint spectroscope was obtained by 

 means of the diffraction images, and that of the quartz was checked in 

 the same manner. 



The length of the spectrum of the flint is 3^ inches from H/s 



