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PHIPPs’S JOURNAL. 565
the great reputation of the author, as well as the very good reafons he offers in favour
of his improvement, were fufficient inducements to me to try the experiment.
In the log which I made ufe of,
The length of the cone was - 12 inches.
The diameter of the bafe < gee
The weight of the cone - 25 ounces.
The diagonal length of thediver = 14 inches.
The length of each fide - - gi.
‘The weight of the diver - - 26! ounces.
The length of line from the diver to the cone, 50 feet: the log line 51 feet toa
knot.
Whether M. Bouguer’s log will (as he expected) correct the errors arifing from
currents in the common log, I had no opportunity in difcovering in this voyage.
The fecond error, which no log will correct, cannot be attended with any bad effect,
as it muft make the reckoning, in whatever degree it takes place, ahead of the fhip.
By obferving M. Bouguer’s rules in comparing it with the common log, which for
that purpofe muft be reckoned at fifty-one feet, it will, I think, very fully correét the
third and fourth, which are the moft material errors; as the agitation of the fea from
winds does not exceed the depth to which the diver is let down, and the weight of the
whole machine prevents the friction of the reel from having an effect in any degree equal
to that which it has on the common log.
The fifth arifes from the imperfe¢ction it has in.common with the log generally ufed.
At firft, on the paflage out, I contented myfelf with heaving Bouguer’s log occa-
fionally, to obferve what precautions were neceflary to be taken to prevent errors, as
well as to find whether its variations from the common log were on the fame fide as the
meridian obfervation required. I found that it was neceflary to take care that the
diver fhould be of fuch a weight as to let only the top of the cone fwim ; but not heavy
enough to fink it, as in that cafe it would be liable to an error in excefs, by meafuring
the depth that the diver would fink in addition to the fhip’s way. It was neceflary to
put a weight of lead to the bottom of the diver, to fink it down to its place before the
{tray line wasout. ‘The line between the diver and the cone fhould not be more than
fifty feet, that being as great a depth as it will fink to whilft the {tray line is running off
the reel when the fhip has much way through the water.
On the paflage out, the longeft period of my trying this log between two obfervations,
was from the twenty-fifth to the thirtieth ; in which time the fhip had run four degrees,
and the reckoning by Bouguer’s log was eighteen miles aftern of the fhip: but as it ap-
pears that the fhip on the twenty-fixth, with the wind northerly, and making barely an
eat courfe, was found by the obfervation to be twenty miles to the northward of her
reckoning, that diftance muft be attributed to a current ; therefore if that current had
not taken place, Bouguer’s log would have been, inftead of eighteen miles aftern, two
_miles ahead of the fhip.
On the paflage home it was tried from the latitude of eighty degrees eleven minutes,
to fixty-eight degrees eleven minutes; in which diftance, though the fhip was much
awed from the fea being frequently upon the quarter, this log was only thirty-one miles
ahead of the fhip, which might be owing entirely to that circumftance without any
other caufe.
The ftate of the common log on the paffage out, when the weather was remarkably
fine, and water in general fmooth, was, from the latitude of fixty degrees thirty-feven
minutes to feventy-eight degrees eight minutes, with the line marked fifty-one feet to
thirty feconds, one degree fifty-eight minutes aftern of the fhip, with the line marked forty-
five
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