'(M*> 
proportional Dilatation and Contradion ; the firft of 
which I take to be very hard to be found in ordinary 
Glafs Canes, and the other I fear (till wants to be 
made out by authentick Experiments. 
The laft contrivance for this purpofe, is that of Mr. Pa- 
trick, who (files himfelf th ^Torricellian Operator, by filling 
a (mail Glafs Cane about five Foot long, and fomewhac,. 
but as little as may be, tapering upwards towards the 
dole end of the Cane ; then inverting it, without a 
flagnant cittern of Mercury, fo much of the Mercury 
as exceeds the length of the Column the Atmofphere 
can then fupport, will drop off, and leave its length 
equal to the then prefent height of the common Baro- 
meter : now when the Barometer rifes, this length in 
the Cane becomes greater by the Mercury s being prett 
up into the upper and narrower part of the Tube; 
and when it falls, on the contrary, it fettles down in- 
to the wider part thereof, and becomes Ihorter, b.eing 
always the fame in Quantity. By this means, as the 
Angle of the Concave Cone of Glafs, of which this 
Tube confifts, is fmaller, the different ficuation of the 
Mercury, will, upon the alteration of the Airs prefiure, 
be nicely (hewn by very large and diffindt divisions. 
Now the ufe 1 would apply this contrivance of the 
Barometer to, is to meafure by it the different Levels 
of Places too remote to be come at by the ordinary 
Inffruments for levelling, w 7 itb the certainty one would 
defire. For this purpofe let there be provided two 
(mail Glafs Canes, as near as can be fimilar, growing 
very little, taper or fmaller at the doled end, (o that 
being inverted, the Mercury may be fufpended in them 
at the height it ought to have at the time of the 
Experiment. Let that height be duly noted, and 
then afeending the Monument, or fome luch Edifice 
where, the afeent may he exa&ly me.alured,lst the Scales 
annexed 
