IL An Account of the Evaporation of Water , 
as it tpas Experimented in Gre(ham CoIIedge 
in the Tear 1^93. With fome Oh fer nations 
thereon. By Edm. Halley. 
IN order to explain the Circulation of Vapour Ex- 
perimentally, I caufed an Experiment of the Quan- 
tity of Vapour arifing fimply from the warmth of the 
Water, without being expofed either to Sun or Wind, 
to be made in Grejham Colledge^ which has been per- 
formed with great Care and Accuracy by Mr. Hmt^ 
Operator to the Society : Having added up into one 
Sum the Evaporations of the whole Year, I find that, 
from a Surface as near as could be meafiired of 8 Square 
Inches, there did Evaporate during the Year, idipz 
Grains of Water, which is 64 Cube Inches of Water , 
and that divided by 8 Inches the Area of the Water s 
Surface, Ihews that the depth of Water evaporated ia 
one Year amounts to 8 Inches. But this is much too 
little to anfwer to the Experiments of the French, who 
found that it rained 19 Inches Water in a Year at farts. 
Or thofe of Mr. Tovonley^ who by a long continued Se- 
ries of Obfervations has fufEciently proved that, in L^»- 
cafhire at the foot of the Hills, there falls above 40 In- 
ches of Water in the Years time. Whence it is very 
obvious, that the Sun and Wind are much more the 
caufts of Evaporation, than any internal hear, or agi- 
tation of the Water. The fame Obfervations do like- 
wife (hew an odd quality in the Vapours of Water, which 
is that of adhering to the Surface that exhaled them , 
Vv'hich they cloath as it were with a Fleece of Vaporous 
Air, which once iovefling it, the Vapour rifes after- 
wards ifi much lefs quantity : which was fhewed by the 
fmall quantity of Water that was loft in 14 hours time, 
E e 1 whtn 
