C 418 3 
we have a tolerable Certainty of, efpecially the firft, 
which may be found by Obfervation, almoft at any 
time the Sun {hall be vifible in or above the Horizon, 
either by an Amplitude or Azimuth 5 but unhappily 
as yet, it is not fo in regard to the Latitude, by any 
certain Method, but what is looked on as too abftrufe 
for common Practice 5 for it is but once in 24 Hours 
that an Obfervation can be made from the Sun, and 
even that Space of Time fo very fhort, that if the 
Horizon fhould then be obfcured, or a Cloud intercept 
the Rays of the Sun, the dead Reckoning is then the 
only Guide, which, in Pad, is little better than grope- 
ing in the Dark. 
Since the Latitude then is our principal Guide at 
prefent, and liable to thefe Obftrudions, it would be 
unneceffary to inlarge on the Advantages that would 
accrue to Navigation from Improvements tending to 
obviate them. As this Invention removes a very ma- 
terial Obftacle, viz. an obfcure Horizon, there remains 
another, which, 1 hope and believe, is not altogether 
impracticable to remove 5 and that is, being confined 
but to one fhort Space of Time for Obfervation, as 
already mention'd * and doubtlefs it would be of great 
Advantage to Navigation, could an accurate Method 
be found for difcovering the Latitude as frequently in 
the Day, as you may that of the Variation. 
But to return to the Inftrument under Conftdera- 
tion, which is founded on this obvious Principle, viz. 
“ That the Surfaces of all Liquids, that have a Com- 
6C munication with each other, though feparated at 
“ any Diftance in their Surfaces, will be in a true 
fc horizontal Plane/' 
The 
