LOG. 883 
plate mud be varioufly inclined, in prafhce, up and down, 
as different velocities may require. This inclination may 
be governed by a fcrew, or by bending the fubltance of the 
plate; any other angle of the fly-wheel, with correfpond- 
ing proportions of the other wheels, produces the fame 
efte6f. 
“ The calculation may be lengthened, or fliortened, or 
varied, by increaling or diminilhing the number of wheels, 
and altering their combinations, agreeably to every per- 
fon’s defire. Thofe parts of the machine which fuft'er 
moll from friftion, and therefore are mod liable to decay, 
fhould be conftrufted of the moft durable fubltance or 
coxpofition, whole qualities will abide the effects of, and 
not be injured by, fait water. 
“As this machine always works under water, it avoids 
many irregularities which would arife from the violent 
agitation of the lea’s furface. 
“ The fly-wheel is fo con (trusted as to be capable of 
being regulated to meet true diftance ; and, being fmall 
and portable, it is eafily taken in for infpejffion, and can¬ 
not retard the (hip’s progrefs; it is properly guarded againft 
choking with fea-weed, or other fubllances; the indexes 
are fecured from violence and diforder; all of which ad¬ 
vantages were never combined in any former attempt to 
meafure diftance by a l'piral wheel. The contrate wheel 
may receive its motion from either end of the fly-wheel, 
but the hind end is confidered as the moft proper. All 
the parts of the machine may be made of brafs, or any 
other proper fubltance not liable to be injured by the ef¬ 
fects of fait water.” 
We have an account, in the Voyage to the North Pole, 
p. 97. of two other logs, which were tried by captain 
Phipps; one invented by Mr. Ruffel, the other by Foxon ; 
both conftrufted upon this principle, that afpiral, in pro¬ 
ceeding its own length in the direction of its axis through 
a refilling medium, makes one revolution round the axis; 
if, therefore, the revolutions of the fpiral are regiftered, 
the number of times it has gone its own length through 
the water will be known. In both thefe the motion of 
the fpiral in the water is communicated to the clockwork 
within board, by means of a fmall line fattened at one 
end to the fpiral, which tows it after the fliip, and at the 
other to a fpindle, which fets the clockwork in motion. 
That invented by Mr. Ruffel has a half fpiral of two 
threads, made of copper, and a fmall dial with clockwork, 
to regilter the number of turns of the fpiral. The other 
log has a whole fpiral of wood with one thread, and a 
larger piece of clockwork with three dials, two of them 
to mark the diftance, and the other divided into knots 
and fathoms, to (how the rate by the half-minute glafs, 
for the convenience of comparing it with the log. This 
kind of log will have the advantage of every other in 
fmooth water and moderate weather; and it will be ufeful 
in finding the trim of a (hip when alone, in furveying a 
coaft in a Angle Ihip, or in meafuring diltances in a boat 
between headlands and Ihoals ; but it is fubjeft to other 
inconveniencies, which will not render it a proper fublli- 
tute for the common log. 
In the Annales des Arts, we have the defcription of a 
log upon the above principle, invented by Mr. le Gnin, 
who introduces his account of it by obferving, that cal¬ 
culations made by the common log can feldom be accu¬ 
rate; becaufe, 1, the plank is not fixed during the pro¬ 
grefs of the Hi ip : a, the progrefs of the veffel is always 
unequal : 3, the pilot may run off the line too quickly 
or too (lowly : 4, a ftrong or a light breeze, at .the mo¬ 
ment when the log is thrown into the fea, may produce 
an error in the reckoning: 5, when feven or eight knots 
are run off, the force of the wind acts upon a furface very 
different from that when the wind is more moderate, and 
when the veffels proceed at the rate of but three or four 
knots : 6, a wave may drive the plank nearer or to a 
greater diftance : 7, pilots commonly omit to count the 
fathoms of line exceeding the number of knots. From 
all thefe di fad vantages, therefore, the pilots frequently 
find themlelvss 100 leagues out of their reckoning. 
Mr. ie Guin proceeds to obferve, that all thefe impeY- 
feftions are corredted by the ufe of his log, which is re- 
prefented at fig. 6. This machine being fattened to the 
item of the fliip by a cord at a proper diftance, the lhock 
of the water caules the fpiral A to turn round on its axis. 
On the Item of this axle is a fcrew, B, which fets in mo¬ 
tion the machinery, C,D,E, F, conftrudted in fuch a man¬ 
ner, that, while the great wheel F makes one turn the 
endlefs fcrew B makes 240,000, and the number of turns 
of the endiefs fcrew is indicated by a needle g on the wheel 
F. This wheel has 100 cogs, the wheel D has 40, and C 
has 60. From thefe ftatements this log may be made of 
the fame proportions, and tried. Thole who make trial of 
it at fea mult take it out of the water when the veffel has 
proceeded one league ; they muft examine to what num¬ 
ber the index of the great wheel points, which will cer¬ 
tainly not have made one turn. This number they muft 
note down; and, to afcertain the utility of the log, they 
fliould repeat their experiments both in moderate winds 
and heavy gales. Suppoling at the end of a league that 
the index points to 88 with a moderate wind, and to 76 
with a high wind, it will be eafy to find the mean of this 
equation, and to confirm, by a calculation, or by this 
meafure of the Ihip’s way, the diftance fhe has proceeded. 
Mr. le Guin made an experiment of about 100 leagues 
with his log: the wheel F gave 20 cogs per league, and 
19 with moderate winds. This log is entirely conftrufted 
of copper. 
Perpetual Log, a machine fo called by its inventor, Mr. 
Gottlieb of London, is intended for keeping a conftant 
and regular account of the rate of a Ihip’s velocity in the 
interval of heaving the log. Fig. 7 is a reprefentation of 
the whole machine; the lower part of which, EFG, is 
fixed to the fide of the keel ; H reprefenting only the 
boundary-line of the Ihip’s figure. EF are the feftion of 
a wooden external cafe, left open at the ends K L, to ad¬ 
mit the paffage of the water during the motion of the Ihip. 
At M is a copper grating, placed to obftruft the entrance 
of any dirt, &c. into the machine. I is a feftion of a 
water-wheel, made from 6 to 12 inches in diameter, as 
may be neceffary, with floatboards upon its circumference, 
like a common water-wheel, that turns by the refiftance of 
the water palling through the channel L K. It turns upon 
a (houldered axis, reprelented by the vertical fedlion at IC. 
When the Ihip is in motion, the refiftance of the water 
through the channel LK turns round the wheel I. This 
wheel, by means of a pinion, is connected with and 
turns the rod contained in the long copper tube N. This 
rod, by a pinion fixed at its upper extremity, is connected 
with and turns upon the whole fyftem of wheels contained 
in the dial of the cafe ABCD. This dial, by means of 
the copper tube N, may be fixed to any convenient place 
on-board the fliip. In the front of the dial are feveral ufe¬ 
ful circular graduations, as follow : The circle at A has a 
hand which is moved by the wheels within, which points 
out the motion of the fliip in fathoms of fix feet each. 
The circle at B has a hand fliowing the knots, at the rate 
of 48 feet for each knot; and is to be obferved with the 
half-minute glafs at any time. The circle between C and D 
has a (hort and a long hand ; the former of which points out 
the miles in land-meafure, and the latter or longer the num¬ 
ber of knots contained in each mile, viz. 128, which is in 
the fame proportion to a mile as 60 minutes to the hour 
in the reckoning. At e, a fmall portion of a circle is feen 
through the front plate called the regijler ; which (hows, 
in the courfe of 24 hours (if the fliip is upon one tack), 
the diftance in miles that fhe has run; and in the 24 
hours the mariner need take but one observation, as this 
regifter ferves as an ufeful check upon the fathoms, 
knots, and miles, Ihown upon the two other circled. A is 
a plate fliowing 100 degrees, or 6000 miles; and this alfo 
acts as another regifter or check; and is ufeful in cafe of 
any 
