I 6 I 



freili pump water than in any other., 

 In clear river water they appear, 

 later, lefs in number and in fize; 

 lefs fo in rain water, and the leafl 

 pf all in boiled water, in ftagnating., 

 and in diftilled water. 



They are not produced by the 

 warmth of the fun rari tying the 

 air adhering to the leaves ; for many 

 kinds of leaves produce them almofl 

 as foon as plunged under water, 

 though the water be very cold, and 

 the leaves warm from the fun-fhine, 

 be plunged in it. 



They do not appear after fun-fet % 

 iX leafl not in any confiderable num- 

 ber; but thofe that already exiil do 

 int fhrink in or difappear by the 

 cold of the night. 



As foon as the fun begins to dif- 

 fuse its warmth over the furface of 

 the earth in the fpring, and to pro- 



