335 
HORO 
midnight XII. This plate may represent the Earth, and 
L, London, or tire place to which the. clock is adapted. 
Around this plate there is an elliptic (hade on the moon- 
plate, the liigheft points of which are marked High-water, 
and the loweft Low-water. As this plate turns round be¬ 
low' the plate N, tliefe points come fucceflively even with 
L, and hand over it at the- times when it is high or low 
water at the given place; which times are pointed by the 
fun S on the dial-plate ; and the plate H, above XII at 
noon, rifes or falls with the tide. As the Sun.S goes 
round the dial-plate in twenty-four hours, and the Moon 
M in twenty-four hours fifty minutes and a half, it is 
plain that the Moon makes only twenty-eight revolutions 
and a half whilft the Sun makes twenty-nine and a half; 
io that it will be twenty-nine days and a half from con¬ 
junction to conjunction. And thus the wire a Ihifts 
over one day of the moon’s age on the fun-plate in 
twenty-four hours. The phafes of the moon for every 
day of her age may be feen through a round hole m in 
the moon-plate: thus, at conjunction or nerv-moon, the 
whole fpace feen through m is black ; at oppofition or full- 
moon this place is white; at either quadrature half black 
and half white; and at every pofition the white part re- 
lembles the vilible part of the moon for every day of her 
age. The black-lhaded fpace N/"F /, on the fun-plate, 
fig. 71, ferves forthefe appearances. N reprefents the new 
moon, F the full-moon, and f her firlt quarter, and / her 
lalt quarter, See. 
The wheel-work and tide-work of this clock are repre- 
fented at fig. 72. A and B are two wheels of equal dia¬ 
meters ; A has fifty-feven teeth, with a hollow axis that 
palfes through the dial of the clock, and carries the fun- 
plate with the Sun S. B has fifty-nine teeth, with a folid 
lpindle for its axis, which turns within the hollow axis 
of A, and carries the moon-plate, (fig. 70.) Both wheels 
are turned round by a pinion C, of nineteen leaves, and 
this pinion is turned round by the common clock-work 
in eight hours ; and, as nineteen is the third part of fifty- 
feven, the wheel A will go round in the twenty-four 
hours,- and the wheel B in twenty-four hours fifty mi¬ 
nutes and a half; fifty-feven being to twenty-four as fifty- 
nine to twenty-four hours fifty minutes and a half very 
nearly. On the back of the wheel B is fixed an elliptical 
ring D, which, in its revolution, raifes and lets down a 
lever E F, whole centre of motion is on a pin at F; and 
this, by the upright bar G, raifes and lets down the tide- 
plate H twice in the time of the moon’s revolving from 
the meridian to the meridian again ; this plate moves be¬ 
tween four rollers RRRR. A contrivance of this kind 
was adapted by Mr. Fergufon to the movement of an old 
watch ; the great wheel of a watch goes round in four 
hours ; on the axis of this he fixed a wheel of twenty 
teeth, to turn a wheel of forty teeth on the axis of the 
pinion C; by which means that pinion was turned round- 
in eight hours, the wheel A in tw'enty-four, and the 
wheel B in twenty-four hours fifty minutes and a half. 
We (hall fubjoin a brief account of turn curious con¬ 
trivances. The firft, for giving motion to the parts of a 
clock by making it to defeend along an inclined plane, 
is the invention of Mr. Maurice Wheeler; and the clock 
itfelf may be feen in Don Saltero’s coftee-houfe at Chelfea. 
DE, fig. 73, is the inclined plane on which the clock 
ABC defeends; this confiits externally of a hoop about 
an inch broad, and two tides or plates Handing out be¬ 
yond the hoop about one-eighth of an inch all round, 
with indented edges, that the clock may not ilide, but 
turn round whilft it moves down. One of thefe plates is 
inferibed with the twenty-four hours, which pals fuccef¬ 
fively under the index LF, fig. 7+, which is always in a 
pofition perpendicular to the horizon, and Ihows the hour 
on the top of the machine; for this realon the lower part 
of tire index, or H L, is heavieft, that it may preponderate 
the other, HP, and always keep it pendulous, with its 
point to the vertical hour, as the movement goes on. 
Inftead of this index, an image may be fixed for ornament 
Vgl. X, No. 664. 
LOGY. 
on the axis g, which with an erefted finger performs the 
office of an index. In order to deferibe the internal part 
or mechanifm of this clock, let LETQ, fig. 73, be the 
external circumference of the hoop, and ff tire fame 
plate, on which is placed the train of wheel-work 1,2,3, 4, 
which is much the lame as in other clocks, and is go¬ 
verned by a balance and regulator as in them. But there 
is no need of a fpring and fufee in this clock ; tlreir ef¬ 
fects being otherwife lupplied. In this machine the great 
wheel 1 is placed in the centre, or upon the axis of the 
movement, and the other wheels and parts towards one 
fide, which would therefore prove a bias to the body of 
the clock, and caufe it to move, even on the horizontal 
plane, for fome fhort diftance; this makes it neceftary to 
fix a thin plate of lead at C, on the oppofite part of the 
hoop, to reftore the equilibrium of the movement. This 
being done, the machine will abide at reft in any pofition 
on the horizontal plane H H; but, if that plane be changed 
into the inclined plane D E, it will touch it in the point 
D ; but it cannot reft there, becaufe the centre of gravity 
at M acting in the direction M 1, and the point T having- 
nothing to fupport it, mull continually defeend, and carry 
the body down the plane. But now if any weight P be 
fixed on the other fide of the machine, fuch as fhall re¬ 
move the centre of gravity from M to the point V, in the 
line LD, which palfes through the point D, it will then 
reft upon the inclined plane, as in the cafe of the rolling 
cylinder. If this weight P be fuppofed not fixed, but 
fufpended at the end of an arm, or veCtis, which arm or 
lever is at the fame time falfened to the centrical wheel 
r, moving on the axis M of the machine, which wheel by 
its teeth (hall communicate with the train of wheels, Sc c. 
on the other fide, and the power of the weight he juft 
equal to the fridtion or refiftance of the train, it will re¬ 
main motionlefs, as it did before when it was fixed; and 
confequently the clock alio will be at reft on the inclined 
plane. But, fuppoling the power of the weight P to be 
fuperior to the refiftance of the train, it will then put it 
into motion, and of courfe the clock likewile; which will 
then commence a motion down the plane; while the 
weight P, its vectis PM, and the wheel 1, all conftantly 
retain the fame polition which they have at firft when the 
clock begins to move. Hence it is ealy to underhand, 
that the weight P, may have fuch an intrinfic gravity, as 
fhall caufe it to a6t upon the train with any required 
force, l’o as to produce a motion in the machine of any 
required velocity; fuch, for inftance, as fhall carry it 
once round in twenty-four hours; then, if the diameters 
of the plates ABC be four inches, it will delcribe the 
length of their circumference, viz. i2 - 56 inches in one 
natural day; and therefore, if the plane be of a fufficient 
breadth, fuch a clock may go feveral days, and would 
furnilh a perpetual motion, if the plane were infinitely 
extended. Let S D be drawn through M, perpendicular 
to the inclined plane in the point D; alfo let LD be per¬ 
pendicular to the horizontal line H H, palling through D ; 
then is the angle HDE = LDS=DMT; whence it fol¬ 
lows, that the greater the angle of the plane's elevation is, 
the greater will be the arch DT; and confequently the 
further will the common centre of gravity be removed 
from M; therefore the power of P will be augmented, 
and of courfe the motion of the whole machine accelerated. 
Thus it appears, that by duly adjufting the intrinfic 
weight of P, at firft to produce a motion Ihowing the 
mean time as near as polfible, the time may be afterwards 
corrected, or the clock made to go falter or flower, by 
railing or deprefling the plane, by means of the ferew at 
S. The angle to which the plane is firft railed, is about 
ten degrees. The marquis of Worcefter is alto laid to 
have contrived a watch that moved on a declivity. See 
Phil. Tranf. Abr. vol. i. p. 4.68, See. 
The other contrivance is that of M. de Gennes, for 
making a clock afeend on an inclined plane. To this 
end let ABC, fig. 75, be the machine on the inclined 
plane EDE, and let it be kept at reft upon it, or in 
4 Q equilibrio, 
