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fame, as well as two that are true. But, admitting 
they were never fo truly made, they are notwith- 
ftanding fubjefl to Error, fince it is but too well 
known, that dry and wet Weather have a great In- 
fluence on them. Should the Half-minute Glafs 
jack but two Seconds, or be two Seconds too long 
it makes an Error of fotne Miles in 24 Hours. If 
the Log be hove by Quarter-minute Glades, in like 
manner defective, (which is the general Practice, 
when the Ship has great Way) in doubling the 
Knots, the Error is alfo doubled. Befides, when the 
Ship runs after the Rate of 8 or 9 Miles an Hour 
(and the Line is left to run off of the Reel) it 
rarely happens but fome Fathoms are out, before 
the Line can be flopp’d } though this may be fmall 
in the Courfeof 24 Hours, and therefore difregard- 
y £t in f Jon S Voyage it will make a great 
Addition to the many Errors in the Diftance (which 
we gain by the Log) which, added to thofe of our 
Judgment, occafions fo many that keep Journals 
at Sea to be a Shore, when they have reck- 
oned themfeives 50, 60, or more Leagues from 
the Land; and others to be as many Leagues 
from their Port, at the Time when they have 
expected to make it. 
“ In the Marine-Surveyor it is not fo: for this In- 
« SinTn fT re u n ° Glaffes , of , an y Kind : Let the 
Ship run faff or flow, it is the fame, for it works in 
Proportion, and the Bell ftrikes to every Mile ar 
“ cordingly. To evidence the Truth of this I take" 
“ Leave t0 mention an Inftance, viz. When I was 
“ making my Experiments on the Canal, the Reverend 
“ Ur- Defaulters, one of the Members of this honou. 
rable Society, and feveral other Mathematicians 
- at llra es, were with me, and we meafur’d out a 
“ certain 
