C 4«< ] 
will be truly Horizontal, conformable to the above 
Principle 5 then keeping your Eye on the central 
Thread, bring that and the little Surface into one, 
which will be effefted with the fame Eafe, as if you 
obferved by the natural Horizon 3 then keep moving 
the End of the Index F, till you bring the Speculum 
of the Sun in the little Hole on the horizon Vane 
that is clofe to the Thread, fo that you have, as it 
were, but one ObjeCt to look at during the time of 
Obfervation : But if you ufe the (hadow Vane, you 
mud bring the upper Edge of the Shadow on the 
central Line, drawn on the horizon Vane, as ufual ; 
remembering as often as you reft, waiting the Sun's 
rifing, to clofe the Slide, which prevents the Water's 
running out, it then remaining immoveable. And 
thus continuing to do, till the Sun is on your Meri- 
dian, caft up the two Sums as is ufual, that is, the 
Degrees cut by the fhadow Vane, and thofe cut by 
the upper Edge of the Index on the greater Arch, 
which Sum will give what is required, viz. the Sun's 
Diftance from the Zenith. On the End of the Index 
is fix'd a fight Vane N, by which you may obferve by 
the natural Horizon, the very fame way as with the 
common Quadrant 3 fo that the one will be the Proof 
of the other. 
N.B. There are of late Invention, large glafs 
Lens’s, very ufeful for collecting the 
weak and fcatter'd Rays of the Sun into 
a Speculum 5 but if the Rays are even too 
weak to be collected by that, and that 
you have any Sight of the Sun, let ano- 
ther look through the little Hole on the 
horizon Vane above- mention'd, and the 
upper 
