672 Col. roy’s Experiments for 
experiments, the tube being wholly covered with boiling 
water, no condenfation of vapour took place in the va- 
cuum; and therefore no particles of quickfilverwere feen 
adhering to the upper part of the tube. When the wa- 
ter boiled, the refiftance of the vapour was greater than 
in the preceding fet, and the total expanlion lefs. Thefe 
two refults ferve ftrongly to confirm each other: it is, 
however, the laft that furnillies the data for conftrudting 
the table of equation depending upon the heat of the 
quickfilver in the barometer, of which table we fhall 
give an account hereafter. 
Finding, from the comparifon of thefe two fets of ex- 
periments with each other, that the maximum and rate 
of expanfion feemed to vary with the length of the va- 
cuum above the quickfilver, I was advifed to try^ what 
might be the refult, when the vacuum was much longer 
than in the common barometer. 
The third fet of experiments of this clafs was there- 
fore made with a tube fomewhat narrower in the bore 
than the former, and whofe vacuum was 1 \\ inches in 
length, whereof 1 reached above the top of the veflel. 
The mean of three obfervations gave .5443 for the total 
expanfion on 1 8o°; that for the firfi: 20 ° w r as .067 ; for 
(d) Dr. blagdeNj who afterwards affifted in fome of the hrft experiments 
with the manometer, propofed that with the long tubf . 
the 
