Total Eclipse of the Sun, 1901, May 18. 257 



graphs were taken of the Sun, on the same plate for orientation. The 

 plate was an Imperial Fine Grain Ordinary and the exposure was as 

 quick as could possibly be given by uncovering and covering the object- 

 glass by hand. The true local times of the three exposures were : 



h. m. s. 



7 58 39 3 



7 58 57-3 



7 59 17-3 



A ninth plate, a Wratten and Wainwright Instantaneous plate, was 

 exposed with the same aperture and exposure at 8 h O m 17 S> 3. The 

 plate in the tenth plate-holder was not used. 



Two sets of " Abney squares " were printed upon No. 4 on June 13, 

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

 of a Sugg's Standard candle, at 5 feet distance ; the one being exposed 

 for 15 seconds, and the other for 4 minutes. 



No. 1 is a clean and fairly dense negative, showing well the polar 

 rays and the structure of the lower corona, especially in the east 

 equatorial wing. The west wing shows less detail. The corona is 

 traceable to a distance of 15 or 16 minutes from the limb of the Moon 

 in the S.E. ray. 



No. 2 is a clear thin negative showing much about the same detail 

 as No. 1. 



No. 3 is a thin negative but shows a considerable extension of the 

 great S.E. and N.E. rays and a good deal of detail in their lower 

 regions. 



No. 4 is a dense negative showing the greatest degree of extension 

 in the coronal streamers of any of the series. In the case of the two 

 chief rays, the corona can be traced to a distance of nearly half a 

 degree from the Moon's limb. 



No. 5 shows the lower corona well up to 5 or 6 minutes from the 

 Moon's limb. 



No. 6 is partly spoiled by fog, and only the lower corona is seen up 

 to about 3 minutes. 



No. 7 is a faint and delicate negative showing the chromosphere, 

 prominences, and the lower corona up to a distance of about 3 minutes 

 from the limb of the Moon. 



Two methods were employed to focus the Greenwich coronagraph ; 

 the first being the method described by the Astronomer Royal in his 

 Reports of the Eclipse Expeditions of 1896, 1898, and 1900,* an 

 image of an object (gauze net in the plane of the plate) being photo- 

 graphed by reflection normally from the plane mirror of the crelostat. 

 The second method was by photographing Arcturus, the image of 

 which was allowed to trail across the platel 



* ' Roy. Soc. Proc.,' TO!. 64, p. 8 ; and ' Monthly Notices, E.A.S.,' TO!. 57, p. 105, 

 and Tol. 60, p. 397. 



VOL. LXIX. T 



