[ 4*4 ] 
Horizon, that could be as effectually relied on, as 
that of the true or natural 5 and at the fame time 
plain, eafy, and obvious j I am of Opinion, it would 
be needlefs to go about proving its Ufefulnefs. 
To this End, fome ingenious Gentlemen have, 
within thefe few Years, very commendably employed 
their Talents this way 5 among which, I humbly offer 
my Mite : And that the Partiality of a Parent to a 
Child of his own begetting, may not carry me too far, 
I fhall moft humbly fubmit it to the Determination 
of that venerable and learned Affembly, who are as 
ready to infpeft, as they are willing to encourage and 
promote, the Inventions of all ufeful Parts of Me- 
chanifm. 
I fhall now proceed to the Principle on which this 
Apparatus is founded, viz. 
That the Surface of all Liquids {when free from 
any external Caufe) that have a Communica- 
tion with each other , though divided and fe- 
farated in their Surfaces , will be truly in a 
horizontal Flain . 
The Quadrant, and its Conftru&ion, being well 
known, there remains but little to be faid to it $ the 
principal Parts that I fhall take Notice of, are the two 
Se&ions of two different Circles that are concentrick, 
a sj 4 B, CD , {fee Tab. I. Fig. 1. ) on which the De- 
grees and Minutes are graduated 5 E, the common 
Centre, through which goes a brafs Pin fix’d to the 
Apparatus EF, which is an Index or Radius to the 
Se&ion CD, on which Index is fix’d a brafs Tube if 
Inches long, in the Extremities of which are fix’d 
per : 
