PHOTOGRAPHS OF THE CORONA. 



105 



person by looking into it could see the cross-hairs up the tube, 

 and also see when the sun was centrally on them. In the photo- 

 graph, I am looking into this mirror as I turn the tangent 

 screw. An ordinary screw held the camera towards the lens end 

 fixed to the stand, while toward the plate end of the camera was 

 fixed a long camera screw, which, acting as a tangent-screw, 

 enabled me to follow the sun and keep it on the cross-hairs. 

 The plates used were Ilford extra rapid red label, half-plate 

 size, thickly backed with Tyler's plate-backing to prevent 

 halation. Six exposures were given ; the first of about J second, 



MR. COUSENS AT JKUR. 



and the others in order J, 1, 2, and 4 seconds. In the 

 middle of the sixth exposure the sun came out. The developer 

 was the Ilford formula, freely diluted with water, and half as 

 much again bromide of potassium as usual. The development 

 was prolonged, and the distilled water used, as well as the 

 developer, were both cooled for a day or two previously by 

 placing wet rags around the bottles. This was very necessary. 

 The shortest exposure brought out too much corona, and half 

 or a third would have been better in order to show the pro- 

 minences. The longer exposures bring out the great streamers 

 very fully. 



HENRY COUSEXS. 



My lens was a Dallmeyer stigmatic lens of 1J in. aperture 

 and 9 in. focal length. With this I hoped to secure the exten- 

 sions of the corona, and consequently intended to give prolonged 

 exposures ; but I had neither equatorial nor driving-clock. 

 Both these w r ere kindly supplied by the Council of the Royal 

 Astronomical Society, who placed at the disposal of my husband 

 the photographic telescope and equatorial which the late 



