. 224 On the Nature and Conftruéiion 
lott to the fun by the emiffion of light, the poflibility of which 
we have been mentioning above, may not be one of thefe 
purpofes, I fhall not prefume to determine. The motion of 
the comet, difeovered by Mr. Meffier in June 1770, plainly 
indicated how much its orbit was liable to be changed by the 
a 
perturbations of the planets; from which, and the little agree-_ 
ment that can be found between the elements of the orbits 
of ali the comets that have been obferved, it appears clearly 
that they may be directed to carry their falutary influence to 
any part of the heavens. ; 
My hypothefis, however, as before obferved, does not lay 
me under any obligation to explain how the fun can fuftain 
the watte of livht, nor to fhew that it will fuftain it for ever ; 
and I fhould alfo remark that, as in the artalogy of generating 
‘clouds, I merely allude to their produétion as owing to a de- 
compofition of fome of the elaltic fluids of our atmofphere, 
that analogy, which firmly refts upon the faé, will not be 
lefs to my purpofe, to whatever caufe thefe clouds may owe 
their origin. It is the fame with the lucid clouds, if T may 
fo call them, of the fun. They plainly exift, becaufe we fee 
them; the manner of their being venerated may remain an 
hypothefis—and mine, till a better can be propoted, may ftand 
good; but, whether it decs.or not, the conlequences I am 
going to draw from what has been faid will not be affected 
by it. | 
Before I proceed I fhall only point out, that, according to 
the above theory, a dark {pot in the fun is a place in its at- 
mofphere which happens to be free from luminous decom- 
pefitions ;, and that facul are, on the contrary, more copious 
mixtures of fuch fluids as decompofe each other. The pen- 
“umbra, which attends the {pets, being generally depreffed,: 
more or lefs, to about half way between the folid body of the 
fun and the upper’part of thofe regions in which luminous 
decompofitions take place, muft of courfe be fainter than 
other parts. No fpot favourable for taking meafures having 
lately been on the fun, I can only judge, from former ap- 
pearances, that the regions in which the Juminous folar - 
clouds are formed, adding thereto the elevation of the facu- 
le, cannot be lefs than 1843, nor mec more than 2765 
miles’ 
