3 8 Vegetable Staticks. 



and trees, in proportion to the greater or 

 lefs convergency of the Sun's rays. 



The learned Boerhaave, in \i\%Theory of 

 Chemiflry, p. 245. obferves, il That thofe 

 " white clouds which appear in fummer- 

 " time, are as it were fo many mirrours, 

 <c and occafion exceffive heat. Thefe cloudy 

 tc mirrours are fometimes round, fome- 

 " times concave, polygonous, &c. when 

 " the face of heaven is covered with fuch 

 " w 7 hite clouds, the Sun mining among 

 " them, muft of neceffity produce a vehe- 

 " ment heats fincemany of his rays, which 

 €C would otherwife, perhaps, never touch 

 < c our earth, are hereby refle&ed to us 5 thus 

 " if the Sun be on one fide, and the clouds 

 " on the oppofite one, they will be per- 

 " feci; burning glades. And hence the phse- 

 " nomena of thunder. 



" I have fometimes (continues he) ob- 

 " ferved a kind of hollow clouds, full of 

 " hail and fnow , during the continuance 

 a of which the heat was extreme 5 fince by 

 " fuch condenfation they were enabled to 

 (C reflect much more ftrongly. After this 

 cc came a (harp cold, and then the clouds 

 l c difcharged their haii in great quantity 5 



to 



