Tvtnl Solar Eclipse of 1900 (Mai/ 28). 359 



It was found later that the faintness of the light was caused by a 

 dark glass in front of the eye-piece, which was used for viewing the 

 image on the slit. This was needed in the first exposures, but should 

 have been removed by turning the hinged glass aside. It is evident 

 from the photographs that the image was improperly adjusted in 

 consequence of the faintness of the light ; there is no impression on 

 the plates. 



The results obtained with the four-prism spectroscope may be 

 summarised as follows : Five photographs of the spectrum of the 

 vapours near the sun's limb at a fixed point, and a photograph of the 

 spectrum of the corona at two points widely separated near the sun's, 

 limb. 



25. T/u; Photographic Camera with Large Objedive Grating. 



Visual observations of the green coronal ring made at Pulgaon, 

 India, 1898, January 22,* convinced me that the ring could have been 

 photographed with the objective grating and telescope then used. 

 Accordingly preparation was made to attempt a photograph with a 

 large grating at Algiers. For this purpose, use .was made of a plane 

 grating by Rowland, 14,438 lines to the inch on a ruled surface- 

 5 x 3^ inches, fitted on an axis in front of a telescope of focal length 

 68 inches and aperture 4 inches. The grating is a very brilliant one,, 

 and is ruled on an unusually fine-grained piece of speculum metal. 

 The object glass is an excellent one by Cooke and Sons. Both of 

 these belong to the splendid spectroscopic installation arranged by the 

 late Professor Piazzi Smyth, with the aid of contributions from the 

 Government Grant. The installation is now set up at the Cambridge 

 Observatory, having been put at my disposal for spectroscopic investi- 

 gations by the Royal Society. I am thereby put under a great obli- 

 gation to the Society, and I venture to take this opportunity of 

 making acknowledgment of it. 



In the recent eclipse the sun was about as far to the north of the 

 celestial equator as it was to the south in the Indian eclipse of 1898 ; 

 accordingly the grating and telescope could be mounted in almost the 

 same relative positions in Algiers as in India ; it was only necessary to- 

 reverse the positions along the polar axis, and arrange that the tele- 

 scope pointed towards the south pole instead of the north. Accord- 

 ingly the instruments were mounted so that the telescope was parallel 

 to the earth's axis and pointed downwards towards the south pole. 

 For the purposes of taking photographs this position was extremely 

 convenient. 



A strong wooden bridge or yoke was fitted to the object glass end 

 of the tube of the telescope, and projected in front of the object glass 



* ' P.oy. Soc. Proc-.,' vol. 61, p. 58 ; and ' Mon. Not., R.A.S.,' vol. 58, App., p. (58). 



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