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ball in very fmall drops. This thread of glafs is 
fattened by the heat given to the tube in making the 
bend next to the ball. In order to fill the fhorter 
leg with mercury, to fit the inftrument for a new 
experiment, it mutt be inclined till the mercury in 
the ball covers the orifice of the tube n. The cy- 
linder being then heated, the mercury will be forced 
into the fhorter leg, and will run down the thread of 
glafs in drops, which will foon unite. By this means, 
luch a quantity of mercury mutt be got into the 
fhorter leg, as, upon the cooling of the inftrument, 
will be fufiicient to drive all the fpirit of wine into 
the ball with a lefs degree of cold than what the 
thermometer is likely to be expofed to. 
The ball A mutt always have feme mercury in it, 
but never enough to fill it up to the orifice of the 
tube ?i. It mutt therefore be made of inch a fize, 
as to contain all the mercury, which can come into 
it from the tube without being too full. If it fnould 
happen to be made too fmall, fo as to be too full in 
cold weather, any part of the mercury may ealily 
be driven into the cylinder, and got back again into 
the ball when wanted in warmer weather. 
It will be better to leave a little of the fpirit above 
the mercury in the longeft leg ; in which cafe the 
top of the fpirit will fhew the common degrees of 
heat. For the filling the tube, fo as to leave none, 
is attended with fome trouble ; and more of it will 
be apt to get up there, if the inftrument ihould hap- 
pen to be held in an improper fituation, or if it be 
kept in too warm a place without filling the fhorter 
leg with mercury by the method above delcribed. 
If too great a quantity fhould get up, tho’ it would 
Vol. 50. Rr not 
