(440 
Parts of Mathematical Science, applied his Thoughts 
to confider the Inftruments ufed in that mod momen- 
tous Part of Bufinefs, Navigation. He faw that on 
.the Knowledge of the Latitude and Longitude of the 
Place a Ship is in, the Lives of thoufands of ufeful 
Subject?, as well as valuable Cargoes, continually 
depend ; that for finding the firft of thefe, certain 
and eafy. Methods are furnifnM by Nature, if Ob- 
fervations be duly made: But Davis * s Quadrant 
Inflrument generally ufed by Britifh Navigators, 
(tho 9 feldom by Foreigners) he perceived was at- 
tended with this Inconveniency, that the Obferver 
nauft bring the Shade or Spot of Light from the Sun, 
and the Rays from the Horizon, to coincide exactly 
on the fiducial Edge of the horizontal Vane: That 
tho’ this can be done in moderate Weather and 
Seas with a clear Sky, and when the Sun is not 
too high, without any great Difficulty^ yet in other 
Cafes it requires more Accuracy than can in fome 
Jun£lures pofiibly be applied, and more Time than 
can be allowed for it. In European Latitudes, or to 
thofe nearer the Northern Tropick, when the Sun 
is in the Southern Signs, and near the Meridian, he 
rifes and falls but flowly : Yet in Voyages to the 
Eaji 2X&.W'eJt-IndieSi of which very many, efpe- 
cially to the latter, are made, he is at Noon, often 
and for many Days together, in or near the Z'enith, 
and when approaching to, or leaving it, he rifes and 
falls, when he has Declination, farter than even at 
the Horizon 5 for it is well known toPerfons ac- 
quainted with the Sphere, that when his diurnal 
Courfe takes the Zenith, he there rifes and falls a 
whole Degree or 60 Minutes, in the Space of four 
Minutes 
