[ 47 3 
fuant to a Theory entirely agreeing with theft Experi- 
ments, that this Method may be employ'd with Cer- 
tainty, for determining the Height of Mountains by 
the Barometer, and reducing the Angies obferved from 
the Tops of theft high Places, to what they would 
be, if they had been obferved on a Plane horizon- 
tal with the Level of the Sea. Now theft new Ob- 
fervations can be made on our Way in tracing the 
Meridian $ and for that Purpofe I have begun to 
conftruft compound Barometers, which, by their pe- 
culiar Make, being very nice, will ftrve to ob- 
ferve with Accuracy the Quantity of the Mercury's 
Fail at the different Elevations to which they fhali 
he carried, in order to fix with greater Certainty the 
Proportion of that Fall. I fhali take particular Care 
in the Conftru&ion and Uft of theft Inftrumeiits to 
provide a Remedy againft the Effect of Heat, which, 
as it is different in the different Times and Places 
of making thefe Experiments, may poffibly produce 
apparent Variations, of which 'tis neceffary to keep 
an Account^ 
There is {till another Method of determining the 
Elevation above the Level of the Sea of all the 
Points, in which the Triangles terminate, that are 
made for the Meafurement of the Earth. This may 
be done by beginning theft Operations near the 
Sea, as I propofe to do, and adually meafuring how 
many Toifts and Feet the Places of. the firfl: Sta- 
tions are elevated above the Level of the Sea. F03* 
if. the Angles of the apparent Elevations of the Ye- 
eond Stations feen from the firft be afterwards ob~ 
ferved. It will be an eafy Matter, from the known 
Diffuses, to deduce the true Elevations of the latter 
