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traftive. To find the courfe made good : Increafe the ob- 
ferved angle between the log-lines by one-fourth part; 
and this gives the correction to be applied to the appa¬ 
rent courfe, or the oppofiteof that lhown by the common 
log; the correction is to be applied to the of 
the apparent courfe, when the bearing of the common log 
is to the j S of the compound log. Or thus: The 
lengths run oft' both logs, together with their bearings, 
being known ; in a card or compafs apply the knots run 
oft', taken from a fcale of equal parts along their refpec- 
tive bearings from the centre; join the ends ; and in this 
line produced, on the fide next the compound log’s length, 
take one-fourth of the interval ; then a line drawn from 
the end, thus produced, to the centre of the card, will 
fhow the true courfe and diftance made good. When a 
current, fuch as a tide, runs to any depth, the velocity of 
that current may be much better afeertained by the com¬ 
pound log than by the common one, provided the diver 
does not defeend lower than the run of the current ; for, 
as thofe ftiips which are deepeft immerged drive failed: 
with the tide ; fo, the diver, by being aCted on below, as 
well as the log on the furface, their joint motion will give 
the total eft'eCi of the current’s motion better than what 
could be derived from the motion at the furface only. 
Alfo, by fuch a compound log, the depth to which any 
current runs may be eafily tried. 
The following is the fpecification of a patent granted 
to Mr. Chefter Gould, of the town of Rome, in the county 
of Oneida, in the Hate of New York, merchant ; for an 
improved log for afeertaining a (hip’s diftance. The pa¬ 
tent is dated May 26, xSoo. 
“ I take a cylinder of brafs, or other materials not li¬ 
able to be injured by fait water, of fuch diameter and 
length as the mechanic may choofe, or the purchafer di¬ 
rect; but one of three inches and a half in diameter, and 
nine or ten in length, is confidered as the moft proper. 
To one end of this cylinder is firmly fixed (by ferews or 
otherwife) a conical head-piece, confiding of a ring of 
brafs, made to fit on one end of the cylinder, and four 
ftrong bars, one end of which is joined to the ring, and 
the other meets at fome diftance from the cylinder, and 
are confined together by a piece of brafs prepared for that 
purpofe, and likewife to affix a ring by which the ma¬ 
chine is towed through the water. Between thofe bars, 
all round the cylinder, are palled a number of fine brafs 
wires, terminating at the fame point, and fecured to the 
fame piece of brafs with the bars ; the ufe of which is to 
prevent the entrance of fea-weed, or any kind of l'ubftance 
that might prevent or obftrudft the working of the ma¬ 
chine ; the wires (liould be as few as is confident with 
that defign, and agreeable to the fize of the cylinder. The 
head of the inftrument will ferew off and on to the main 
cylinder, for the purpofe of taking out the fly-wheel 
to regulate. A fly, which may confift of two or more 
vanes of copper, or other materials, is fufpended within 
the cylinder, by means of two bars which crofs the infide 
of it, and are affixed by ferews, which pafs through the 
cylinder into the bars, or may be hung in a frame of any 
fuitable materials, made to fit the infide of the cylinder, 
to which it may be affixed by ferews. This wheel mult 
move freely about its axis, and is ufually about half the 
length of the cylinder ; but the length may be varied, and 
the principle remain the fame. When this machine is 
towed after a (hip, a column of water palfes through the 
cylinder with a velocity always proportioned to the velo¬ 
city of the fhip. This wheel, which is fixed with its axis 
nearly in the centre of the tube, prefents itfelf endways 
to the water, and takes motion from the winding or an¬ 
gular pofitior. of the vanes, on the fame principle as a 
windmill, or fmoke-jack. The diftance this wheel will 
move at each revolution will be in exaft proportion to the 
quantity of angle by which the vanes are removed from 
a parallel with the axis; increafing the wind or angle will 
G. 
occafion a revolution of the wheel in palling over a (horter 
(pace ; and decreafing the angle will occafion a revolution 
in palling over a longer fpace ; hence it is evident, that 
the machine may be regulated by increafing or decreafing 
the angular or winding polition of the vanes. The angle 
muft not be too great, for then the wheel will have too 
much motion in fwift failing; nor muft it be too fmall, 
for then it will want ftrength in (low failing. If the an¬ 
gle equals the twentieth part of : circle, or eighteen 
degrees, then the wheel will run twenty times its length 
at each revolution ; if it equals the thirtieth part of a cir¬ 
cle, or twelve degrees, then it will run thirty times its 
length at each revolution, let the length of the wheel be 
what it may ; and fo of any other angle, whether greater 
or lefs. The vanes fhould be ftrong, and firmly lecured to 
the axis, to prevent their fpringing or Ihifting in ufe, 
which would wholly diforder the calculation or account. 
The vanes being firmly fecured to the axis in nearly the 
like polition or angle intended by the artift, they may be 
regulated to true diftance by fpringing or bending their 
lubftance a little, which will be known by experiment 
at any given diftance. The inftrument, being once ad- 
jufted, will remain accurate till it is worn out. This 
mode of regulating the wheel is confidered the beft, be- 
caufe it is the molt fimple, and much more fecure in prac¬ 
tice than any mechanical method of adjulting the vanes. 
The angle which would be found true in theory muft be 
a little increal'ed, to overcome fri&ion, and the obltruc- 
tion of fuch parts of the machine as break the force of the 
water; this increafe can only be known by experiment. 
On the axis of this wheel, and before the bar which fuf- 
pends the hind part of the wheel, is a pinion-head of eight 
leaves; this moves a contrate wheel of ninety-fix teeth, 
the pinion of which (lands acrols the cylinder; the cylin¬ 
der (hould extend back fo as to cover this wheel, to de¬ 
fend it from injury. The other wheels, five in number, 
are contained in a line, between two narrow plates, in as 
fmall compafs as can confift with ftrength ; the under 
plate is nicely fitted to fit on the cylinder. Thefe five 
wheels and plates are attached to the cylinder by two 
ferews, through the two ends of the under plate, length¬ 
ways, and in l'uch manner as to receive the pinion of the 
contrate wheel through the cylinder and under plate into 
the upper plate, that it may give motion, by fix leaves, to 
the firft wheel of thirty-fix teeth, contained between' the 
plates. The four lalt wheels have fixty teeth each, and 
are all moved by pinions of fix leaves; each of thefe wheels 
carries an index round a circle, graduated into ten equal 
parts. The circles (hould be as large as they can be con- 
ftrucled without interfering with each other; and thele 
graduations are numbered from one to ten; and the num¬ 
bers on the feveral circles are reverfed, beeaui'e the wheels 
move contrary ways. If the fly-wheel is regulated, which 
in this calculation will equal about one twenty-fourth 
part of a circle, or fifteen degrees, then will the fly or firft 
wheel take one revolution for every eight feet and a quar¬ 
ter that the machine moves through the water, the fe- 
cond every fix rods, the third every thirty-feven rods, the 
fourth every three hundred and feventy rods, or a mile, 
fea-meafure, the fifth every ten miles, the fixth every hun¬ 
dred miles, and the l’eventh every thoufand miles. See. Al¬ 
though I have, in this inftance, preferred a train of wheels 
and pinions, for the purpofe of giving the requifite mo¬ 
tion to the indexes, yet it is obvious that wheels driven by 
endlefs ferews would anfwer the fame end. The wheels 
on the outfide of the cylinder are fecured from violence 
by a cafe of brafs, attached to the cylinder by ferews, and 
prepared with a Hiding cover for conveniently infpefting 
the indexes. The machine is preferved in an horizontal po- 
fition by a plate of brafs, attached to the cylinder on the op- 
polite fide from the machinery. This plate extends about 
two inches back of the cylinder, and terminates in a point 
forward. The weight of the machinery on one fide, and 
the aftion of the plate on the other, keep the machine 
always one fide up, and fufficiently horizontal. This 
3 plate 
