256 Dr. dobson’s Obfer vat ions on 
years with two veffels of equal dimenfions, one placed ort 
the ground, and the other eighteen yards higher on the 
battlement of the hofpital ; that the quantify received in 
the lower veffel exceeds that in the higher more than 
one-third and lefs than one-half. 
6. An ingenious friend, on perufing thefe obferva- 
tions, alked, “ Whether the fad: of evaporation going on 
u equally well in an exhaufted receiver, was not an un- 
“ furmountable objection to that theory concerning eva- 
u poration, which fuppofes a chemical folution of water 
M in air?” With a view to afcertain this fad. I made the 
following experiment. 
Two china faucers, each containing three ounces of 
water, were accurately weighed. One of them wa3 
placed in the open air ; the quickfilver in. the thermo- 
meter Hood duiing the experiment between 48° and 50°, 
the day tolerably clear with a moderate breeze. The 
other was put under the receiver of an air-pump; the air 
was exhaufted, and the piftons occafionally worked, to 
draw off any of the water which might be fuppofed to 
be converted into vapour. After four hours the faucers 
were again accurately weighed; that in the open air had 
loft one drachm and eight grains; the weight of the 
other was not lcnfibly dimin.iihed, 
Froni: 
