SUGGESTIONS TO ASTRONOMERS. 367 
simply to observe, with the weakest of the dark glasses or (if 
possible) with the eye uncovered, and to note the way in which 
the light is distributed, as to intensity, in different directions 
round the sun; whether there are beams of light, and in what 
direction ; whether there are the rudiments of a ring round the 
moon; whether there is any light on the side opposite the bright 
lune. It is recommended that he do not quit this observation 
for any other; but if a trustworthy person of good general obser- 
vation 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 com- 
mence 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 atmo- 
sphere. 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 com- 
pletely 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 ex- 
amined 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 ob- 
server with the most powerful telescope should watch for the ap- 
pearance of red prominences in the direction of the moon’s advance. 
From this time tg the end of the totality each of the observers 
should repeatedly examine the whole circumference of the moon, to 
discover whether there are any of these prominences visible. The 
observer with the most powerful telescope should devote himself 
entirely to this subject. If any are seen, it is of the utmost im- 
