[ 29a ] 



evaporation nearly proportional to the furfaces, in free contad 

 with the air. 11 Coll. Acad. 142, 143, and 146. 



The influence of free contad with the. air is farther illuRratcd 

 by the experiments of the Reverend Mr. Williams of Bradford, in 

 New England, for having filled with water two cylinders of equal 

 diameters and depth, and fupplying the quantity evaporated from 

 one of them once a week, and that evaporated from the other 

 once a month, he found the evaporation from that filled once a 

 week one-third greater than that from the cylinder filled once a 

 month, in the hotter feafon of the year, and fomcwhat belov/ 

 one-third in the colder. 2 American Tranf. p. 118. The reafon 

 of which difference was, that the evaporation during a month 

 teing greater than that during a week, the air during the laft 

 three weeks of each month was obliged to fink deeper into the 

 veflel than during the firft week ; it was therefore more confined, 

 and could not be fo quickly renewed, as that over the vefiTel that 

 was kept full every week ; and therefore during three weeks in 

 each month its evaporation was checked. His vefl"els, though in 

 fome degree expofed to the air and fun, were fheltered from the 

 rain, and therefore in fome degree from the open air. It Ihould 

 alfo be remarked, that according to the beautiful experiments of 

 t)o<£lor Prieftly, common water expofed to the fun, for fome time 

 yields oxygen air, which accelerates evaporation v.hile this pro- 

 duction 



