᾿ 
: 
SUGGESTIONS TO ASTRONOMERS 
FOR THE 
OBSERVATION 
OF THE 
TOTAL ECLIPSE OF THE SUN, 
ON JULY 28, 1851. 
1. Tue principal observations for which a total eclipse of the sun 
presents peculiarly favourable opportunities may be classed under 
the following heads :— 
Observations applying specially to the physical structure 
of the sun and moon, as those of the corona, and of the rose- 
coloured prominences (seen so markedly in the eclipse of 
1842). 
Photometric, thermometric, and actino-chemical observa- 
- tions, illustrating the difference in the nature and amount of 
radiation from different parts of the sun’s disc. 
Optical observations, particularly on the state of polariza- 
tion of the light in different phases of the eclipse, and on the 
phenomena of irradiation, and of distortion of a dark limb by 
the formation of beads or threads. 
The phenomena of the first class have never been seen except in 
a total eclipse of the sun ; and they appear so deserving of attention 
(especially the red prominences, which, if belonging to the sun, indi- 
cate physical peculiarities of structure on a most stupendous scale, 
and perhaps of corresponding importance), that it seems highly desi- 
rable that the arrangements for observation should be planned with 
“especial reference to them. For the observation of the phenomena 
of the other classes, the opportunities (though absolutely rare) are 
