[21 ] 
article; for would it not hence follow, that every 
fpot, having a nucleus, fhould alfo have an umbra 
furrounding that nucleus, a natural account being 
at the fame time fuggelted, for the boundary be- 
twixt the nucleus and umbra being always dif- 
tin city defined, as mentioned in the fecond ar- 
ticle. 
Although we may never have a competent no- 
tion of the nature and qualities of this fhining and 
refpiendent fubftance, or of the means by which 
the excavations in it are formed ; we however 
difcover, in their production, the agency of fome 
mighty, though unknown, caufe, which is there 
often exerting itfelf. Although we manifestly 
behold its effeCts, yet the mode of its operations 
may perhaps remain unfearchable. But if we 
were here to. venture a conjecture, might we not 
fuppofe, that the luminous matter is fo difturbed,. 
and the excavations in- it occafioned, by the 
working of fome fort of elaftic vapour, which is 
generated within the dark globe? And might not 
this elaftic principle, by its expanfion, fwell into, 
fuch a volume, as to reach up to the lurface of the 
-luminous matter, which would' thereby be fepa- 
rated and laid abide in all directions ? And for as. 
much as there is no regularity in the time of a 
fpot’s enlarging, compared to the time of its.de- 
creafing, fome enlarging quickly, and decreafing 
flovvly, and vice vcrja, may we not imagine, that 
this is owing to the duration and quantity of the 
elaftic principle now mentioned ? and in general, 
may we not from hence form fome idea of the 
production and fubfequent enlargement of a fpot, 
as mentioned in the 3d article.? 
But 
