I « 7° ] 
Deviation or Error to be 15 Seconds too flow; by 
Which means it was as ufeful to me for all Purpofcs, 
as if it had gone moft conftantly true without any 
Change. This Watch I kept in my Fob in the Day, 
and in Bed in the Night, to preferve it from the Se- 
verity of the Weather; for I obferved, that all other 
Watches were fpoiled by the extreme Cold. 
I have found, from repeated Obfervations, a' Me- 
thod of obtaining the true Time of the Day at Sea, 
by taking Eight or Ten different Altitudes of the 
Sun or Stars, when near the Prime Vertical, by Mr. 
Smith’s or Mr. Hadleys Quadrant, which I have 
pradifed thefe Three or Four Years paft, and never 
found from the Calculations, that they differed one 
from another more than 10 or 15 Seconds of Time. 
This Certainty of the true Time at Sea is of greater 
Ufe in the Pradicc of Navigation, than may appear 
at firft Sight; for you thereby not only get the Va- 
riation of the Compafs without the Help of Altitudes, 
but likewife the Variation of the Needle from the 
true Meridian, every time the Sun or Star is feen to 
tranfit the fame. Alfo having the true Time of Day or 
Night, you may be fure of the Meridian Altitude of 
the Sun or Star, if you get a Sight 15 or 20 Minutes 
’• before or after it paffes the Meridian ; and the Latitude 
may be obtained to lefs than Five Minutes, with fe- 
veral other Ufes in Aftronomical Obfervations ; as the 
Refradion of the Atmofphere, and to allow for it, 
by getting the Sun’s apparent Rifing and Setting, 
which any body is capable of doing, and from thence 
you will have the Refradion. 
If we had fuch a Telefcope contrived as Mr. Smith 
recommends to be ufed on Shipboard at Sea, now 
we can have an exad Knowledge of the true Time of 
the 
