3 8 Vegetable Staticks. 
and trees, in proportion to the greater or 
lefs convergency of the Sun's rays. 
The learned Baerhaave, in KuTheory of 
Chemiftry, p. 245. obferves, That thofe 
white clouds which appear in fummer- 
time, are as it were fo many mirrours, 
and occafion exceffive heat. Thefc cloudy 
“ mirrours are fometimes round, fome- 
times concave, polygonous, &c. when 
the face of heaven is covered with fuch 
white clouds, the Sun fhining among 
them, muft of neceffity produce a vehe- 
ment heat 5 fmee many of his rays, which 
would otherwife, perhaps, never touch 
our earth, are hereby reflefJed to us , thus 
if the Sun be on one fide, and the clouds 
on the oppofite one, they will be per- 
fed burning glaffes. And hence the phac- 
nomena of thunder. 
I have fometimes (continues he) ob- 
ferved a kind of hollow clouds, full of 
hail and fnow , during the continuance 
of which the heat was extreme 5 fince by 
“ fuch condenfation they were enabled to 
refled much more ftrongly. After this 
came a fharp cold, and then the clouds 
difeharged their hail in great quantity 5 
to 
