[ 4*1 ] 
coincide therewith, proceeding in the fame .manner 
as before, with the Sun. 
v There are two very oppofite Caufes of an obfcure 
Horizon 5 the one proceeds from thick hazy Weather, 
and the other from fine, clear and calm Weather, as I 
have often experienced at Sea : I have been running 
with a Frefh of Wind, fometimes five, fix and feven 
Days together, the Diftance of 2 or 300 Leagues, 
without an Obfervation j and on the fixth, feventh or 
eighth Day, it has proved ftark calm and clear W ea- 
ther, but the Sea fo fmooth, and fo like in Colour to 
the Sky, that the Edge or Circle of the fenfible Hori- 
zon could not be diftinguifhed therefrom, and confe- 
quently no Obfervation to be made by the Inftruments 
then in Pra&ice. 
By this Improvement to ‘Davis’s Quadrant, the 
above Obftacles are intirely removed 5 fo that an Ob- 
fervation can be made off of Headlands, in Harbours, 
on Shore, and, in fhort, anywhere that a Sight of the 
Sun, &c. can be obtained, without any regard had to 
the Horizon 5 and, what is peculiar to it, is, that the 
true Level will be preferved, as well on the Top of 
the higheft Mountain, as clofe to the Surface of the 
Horizon. The Apparatus is fo contrived, that an Ob- 
fervation can be made with the fenfible Horizon as 
ufual, by means of the Sight Vane j\ 7 , fixed near the 
End of the Label for that Purpofe, fo that the one will 
be a Proof to the other. 
As the Succefs of Inventions in all things of this 
kind muft be confirmed by Experiments only, among 
many others, two were effe&ually made on board his 
Majefty’s Ship the Oxford at Spithead } in a high Wind, 
I i i when 
