ving loft nothing fenfible by Evaporation during the Ex- 
periment, which I attribute to the length of the Neck 
wherein the Vapors were condenfed into Drops before 
they reached the Top. Then I examined how much 
Water would raife that in the Neck to the Mark where- 
to it had been encreafed by boiling, and found it was 
a twenty fixth part of the bulk of the firft Water, which 
upon repeated Experiment I found to be true ; but it 
was obvious that Water, encreafing fo very little with 
all the degrees of Heat the Air receives from the 
Sun, was a very improper Fluid to make a Thermometer 
withal ; and befides, any freezing Liquor is ufelefs for 
this purpofe in thefe Northern Climates. 
II. I took a fmaller Bolt- head with a proportional Cane 
or Neck, and filled it, after the fame manner, with Mer- 
cury , and having boiled it as above, I obferved that 12,5- 
Ounces of Mercury had encreafed the fpace of 810 
Grains, or a Seventy fourth part of its bulk when Cold. 
But it was very remarkable, that whereas a gentle Heat 
had fcarce any effect on Water, here on the contrary, the 
Mercury did lenfibly alcend at firft,and had almoft attain- 
ed its greateft Expanfion before the Water boiled in the 
Skillet. And after it boiled, though I let it ftand very 
long over the Fire, I could not difcern that the moft 
vehement boiling had any efFedt on it, above what ap- 
peared when it firft began to boil : The Mercury being 
taken out, as it cooled fubfided, and in a few Hours re- 
turned to the Mark whereat it flood before it was put in- 
to the Water. This Fluid being fo fenfible of a gentle 
Warmth, and withal not fubjedt to evaporate without a 
good degree of Fire, might moft properly be applied to 
the Conftrudioa of Thermometers were its Expanfion 
more confiderable. 
However fmall as it is, it is fufficient to difturb the 
precife nicety of the Mercurial Barometers, fhewing the 
counter poife of thePrelTure of the Atmofphereby a Cy- 
linder 
