CLOCK. 
Asmall circlfe is placed above the great one, 
and divided into 60 parts for the seconds. 
This clock was wound up by a line going 
oyer a pulley and ratchet, on the axis of the 
great wheel, by which the weight was drawn 
up in the same manner as in the common 
wooden clocks. Many of tliese clocks have 
been made, which are found to measure 
time exceedingly well. 
The small imperfection in this clock, of 
its leaving the uncertainty mentioned as to 
which of three hours it denotes, though so 
easily corrected by the judgment, has given 
rise to some ingenious contrivances to ob- 
viate it. 
That of Mr. Ferguson is best known, in 
which tlie hours were engraved on the face 
of the lower great- wheel ; the seconds on that 
of the upper or swing- wheel ; and the minutes 
were shewn in a fixed dial outside all, 
through holes cut in which, certain small 
portions of the other two moveable dials 
were exhibited; the minute-hand was at- 
tached to the axle of the second great 
wheel, which contained 120 teeth, as well 
as the first great wheel; the swing wheel 
had 90 teeth, the axis of the second great 
wheel carries a pinion of 10 leaves, and that 
of the swing wheel a pinion of 6 leaves. But 
this clock had several imperfections, from 
which Dr. Franklin’s clock is free. The 
smallness of the teeth of the swing wheel 
caused the pendulum to describe smaller 
arcs than it should do; the weight of the 
flat ring, on which the seconds were engrav- 
ed, loaded the axis of the swing wheel, so as 
to cause much friction in this part, which 
should be as free from it as possible, and 
there was a considerable difficulty in ad- 
justing the hour plate so as to correspond 
with the minute hand. 
Another very ingenious contrivance for 
the same purpose has been made in a clock, 
on Dr. Franklin’s principle, in the posses- 
sion of Mr. Patoureaux, clock-maker, War- 
dour-street, to which the tubular pendulum, 
on Chandler’s plan, before mentioned, is 
lannexed. To the axis of the great wheel of 
this clock two concentric plates are annex- 
ed, the external one of which has a groove 
cut through it, along the line of a volute of 
four revolutions. This groove forms a 
trough in wliich a metal ball is placed, part 
Of which is seen through its excavations. As 
the plate and groove turn round the ball 
rolls along the volute, still approaching 
nearer the centre as it proceeds ; and when 
at last it arrives at the centre it falls into 
another trou^, by which it is agiain convey- 
ed to the external part of the volute ; the 
hours are engraved between the revolutions 
of the volute ; and the minutes are marked 
on an external fixed circle, to which an in- 
dex, annexed to the volute plate, points. 
We have not been able to discover who is 
the author of this ingenious invention. It is 
certainly a superior method to Ferguson’s. 
The moveable dial being in it annexed to 
the axle of least motion, where of course its 
weight is of least consequence ; and tlie ad- 
justment for the hours and minutes being 
performed in it at the same time. This 
clock is formed with a dead beat escape- 
ment, and is intended for a regulator. 
■ The description of the parts of an eight 
day clock, moved by weights, inserted a 
little farther on, with reference to the an- 
nexed plate, may serve with a little addition 
to give an idea of the mechanism of a clock 
moved by a main spring. 
The spring, by which a clock is moved, 
consists of a long flat plate of steel coiled up 
in a spiral form ; it is inclosed in a cylin- 
drical box, to which its external extremity 
is attached, while its internal end is con- 
nected to a fixed axis, round which the 
spring-box revolves. As the strength of the 
spring is greater the more it is cqiled up by 
turning round the box, its action would be 
unequal in impelling the work of the clock ; 
and to remedy this inconvenience the fusee 
wheel has been contrived. The fusee con- 
sists of a conical barrel, round which ap 
helical groove is cut, that receives a chain 
or catgut, previously wound round the 
spring box, by which, as it is turned round, 
it coils up the spring ; the groove receives 
the chain first near the base of the cone, 
and as tlie barrel revolves, gradually brings 
it nearer the axis ; by this means the stronger 
the spring is coiled up the shorter is the lever 
by which it acts on the work ; and as it gra- 
dually uncoils and becomes weaker, on the 
conti-ary the lever of action becomes longer* 
If instead of the barrel, in figure 2, on 
which the catgut from the weight is coiled, 
the fusee wheel described, be supposed to 
be substituted, and the spiral spring, and its 
barrel and chain to be added, a good idea 
vrill be obtained of a spring-clock; as all 
the rest of tlie work may be the same as in 
the figure. 
Spring-clocks are generally used in cham- 
bers, in places where weight-moved clocks 
would take up too much room. They are 
often so constructed that their frames do 
not hide any part of the work, and are then 
inclosed tt’ith glass covers, so that all their 
