Total Eclipse of the Sun, 1901, May 18. 



255 



(1.) Plwtographs on the 8-inch Scale. 



These were taken by Mr. T. F. Claxton with the photoheliograph of 

 the Royal Alfred Observatory, Mauritius, the object-glass of which is 

 4 inches in aperture and 5 feet in focal length. It gives an image of 

 the Sun nearly 8 inches in diameter, being fitted with a secondary 

 magnifier, enlarging the image in the primary focus 13| times. The 

 total length of the photoheliograph was 9| feet ; its equivalent focal 

 length 69 feet. The camera was constructed to carry plates 10 inches 

 square, and it was proposed to expose six plates during totality for 

 photographs of the corona, and as many as possible during the partial 

 phase for determination of the Moon's place, and of the relative 

 diameters of the Sun and Moon. Only three plates were exposed 

 during totality, the handle of the shutter of the fourth plate-carrier 

 breaking short off when the shutter was opened. The plate-carrier 

 was thus locked in the camera, and it was not possible to release it 

 until the total phase was over. The three plates taken were exposed 

 as below, the exposures being given by Mr. Rowden at the object- 

 glass of the instrument at the sound of the signal bells. 



After totality the clock of the ccelostat was stopped, and three 

 photographs of the Sun were taken on the same plate for orientation. 

 The true local times of the first and last of these were : 



h. 



m. 

 15 

 16 



s. 



20-1 

 5-2 



The time of the second exposure was not recorded. The plate was 

 an "ordinary lantern" by Cadett and Neale. The aperture of the 

 photoheliograph was reduced to 1 inches, and the exposure was 

 given by the drop-slit in the primary focus. 



Two sets of " Abney squares " were printed upon No. 3 on June 13, 

 before the plate was developed. Both sets were printed by the light 

 of a Sugg's Standard candle ; the one being exposed for 4 seconds, the 

 other for 64 seconds, the candle being at a distance of 10 feet in both 

 cases. 



The corona is seen only on the E. side of the Sun, as the image is 



