162 Suggestions for the Observation 



worthy person of good general observation were near, it 

 would be desirable that he should remark whether there 

 appears to be any fluctuation or trembling of the light which 

 falls upon the ground and upon walls, and whether the shadow 

 appears, as to sense, to sweep over the earth. 



17. The important use of the photographic apparatus will 

 commence shortly before the total obscuration. It will be 

 desirable to take photographic images of the cusps, but it will 

 be particularly desirable that they should be varied by causing 

 the pencil of light to pass through a prism, so as to produce 

 prismatic dispersion in the direction transverse to the cusp, 

 and thus to exhibit on the plate or paper an actino-chemical 

 analysis of the light which has passed at the highest degree 

 of obliquity through the sun's atmosphere. When the sun 

 is totally hidden, simple images should be taken, at several 

 repetitions, if possible, during the obscuration. 



18. On the instant of total obscuration the corona will be 

 formed. It is important that the observer with the low- 

 power telescope and the observer with the naked eye should 

 be prepared to remark whether any part of the corona is 

 visible before the sun is completely obscured, and in what 

 order the complete ring is formed, whether all at once or by 

 progress from one or more points. Also, whether the ring 

 is equally broad in different parts, and what is the proportion 

 of its breadth to the moon's breadth ; whether it is double, 

 or divided as a succession of annuli ; whether it is divided 

 by radial lines ; whether its texture appears fibrous, and what 

 is the position of the fibres ; whether it is sensibly coloured ; 

 and, if possible, whether its light is polarized. The light 

 should be examined by the dispersive prism, and the excess 

 or deficiency of any particular colour recorded. 



19. As soon as possible, and also as late as is prudent 

 during the obscuration, an attempt should be made to judge 

 whether the corona is concentric with the moon, or with the 

 sun. 



20. The moment that the sun's bright edge is eclipsed, 

 the observer with the most powerful telescope should watch 

 for the appearance of red prominences in the direction of 

 the moon's advance. From this time to the end of the 



