Report of the Committee , 8c c. 817 
and fecondly, that fo much of the quickfilver in the 
thermometer as is contained in the tube, is more heated 
in the method ufed by fome perfons, than in that ufed by 
others. To fhew that this laft circumftance ought by no 
means to be difregarded, fuppofe that the ball of a ther- 
mometer be dipped into boiling water as far as to the 
freezing point, and confequently that the length of the 
column of quickfilver in that part of the tube which is 
not immerfed in the water be 180°; and fuppofe that 
the heat of that part of the column of quickfilver be no 
more than 1 1 2 0 . If the thermometer be now intirel y 
immerfed in the water, the heat of this column will be 
increafed ioo°; and confequently its length will be in- 
creafed by ^ parts of the whole, as quickfilver ex- 
pands -rfzz P art °f its bulk by each degree of heat; and 
confequently the thermometer will Hand or ra- 
ther more than i°~ higher than it did before. 
Another thing to be confidered in adjufting the boil- 
ing point is, that if the ball be immerfed deep in the 
water, it will be furrounded by water which will be com- 
than it really is, Mr. de lug lias fince, by a great number of experiments 
made at very different heights above the level of the Tea, found a rule by which 
the difference in the boiling point, anfwering to different heights of the baro- 
meter, is determined with great exa&nefs. According to this rule the altera- 
tion of the boiling point by the variation of the barometer from 29! to 30^ 
inches is i°.59 of Fahrenheit, 
Vo l. LXVIL 5 K 
preffed 
