CLOCK. 
wards this improvement about the year 
1715, by the celebrated George Graham, 
HI the contrivance of the dead-beat escape- 
ment, which is principally distinguished 
from the anchor escapement by having no 
recoil. This is effected by increasing the 
depth of the pallets in the line towards 
the centre of the swing wheel, and so 
forming the teeth of that wheel, that the 
pallet in action, in its descent, does not 
touch the teeth at all, but lies between 
them, and the tooth that impels it only 
comes in contact with its inclined plane at 
the instant previous to its ascent, when the 
opposite pallet becomes free. To avoid 
the wearing out of the parts most in action, 
and the influence of friction, the best 
clocks of this construction have swing 
vvheels of hardened steel, with pallets of 
ruby or agate. 
The dkached escapement completed 
the improvement of this part of clock- 
work. Its object is to make the pendulum 
perfonn the greatest part of each vibration 
entirely free from contact, or connec- 
tion, with any part of the train. To effect 
tliis, a catch, or locking piece, restrains all 
the motion of the swing wheel, till the in- 
stant when the pallet is to be impelled by 
it, when it raises the catch, sets the wheel 
free, and is driven forward by its impulse ; 
immediately after which, the catch again 
fells into its place. A great variety of es- 
capements have been contrived on this 
principle by various ingenious men ; those 
in which springs are used in the locking 
pieces instead of pivots, invented by Ar- 
nold, seem now most preferred. 
The detached escapement was applied 
first to chronometers, or time-pieces, but is 
now used for astronomical clocks. From 
the best accounts, Julien Le Roy invented 
the first about 1748 ; since that time, Grig- 
non, Mudge, Cummins, Nicholson, and Ar- 
nold, have contrived various escapements 
of this kind in England ; and Peter Le 
Roy, Sully, Du Tertre, De Bethune, Le 
Paute, Arnaut, Robin, Berthoud, &c. on 
the continent. See Chronometer. 
In the year- 1715, Mr. George Graham, 
before mentioned, made a most material 
improvement in pendulums, by affixing an 
apparatus which tended to raise the centre 
of gravity of the whole as much as the 
lengthening of the rod by heat tended to 
depress it; this he performed by substitu^ 
ing a glass cylinder, containing mercury, 
for the pendulum ball. He afterwards sug- 
gested the idea of using the opposite expan- 
sions of different metals, as a compensation 
for the effects of variation of temperatme of 
the air in pendulums, which was directly af- 
terwards adopted by Harrison, at that time 
an obscure carpenter in the village of Bar- 
ton, Lincolnshire, who surprised the world 
with the invention of the gridiron pendulum 
on this principle. 
In Harrison’s pendulum five bars of steel 
and four of brass were so arranged, that 
they produced two expansions of brass up- 
wards, and three of steel downwards, so 
proportioned to each other, that the ascend- 
ing expansions fully compensated those in 
the contrary direction. This pendulum has 
been since its invention generally used, 
where very accurate measurement of time 
was necessary, A further description of it, 
of Elliot’s pendulum, (which was the next 
made on this plan, and differs little from it)f 
and of the others here mentioned, will be. 
inserted under the article Pendulum. 
It has been supposed by several, that tha 
tubular pendulum, (which is also a modifica- 
tion of Harrison’s compensation) is but a 
very recent invention : but the writer of this 
article having met with one by accident 
which was made upwards of thirty years 
ago, thinks it but justice, both to the pub- 
lic, and the ingenious artist who directed its 
construction, to oppose this opinion. This 
pendulum is in possession of Mr. Patom-eaux, 
watch and clock-maker, 15, Wardour Street. 
It was made by Mr. William Brown, a 
clock-maker well known to the trade, who 
has been dead upwards of five yearn, and 
who formerly resided near the Seven Dials. 
His brotlier, a jeweller, residing in 15, Co- 
ventry Court, Haymarket, was his executor, 
and sold the pendulum to Mr. Barrett, 
clock-maker, of Compton Street, some 
years ago, from whence Mr. Patoureaux 
bought it. Mr. Brown, the jeweller, in- 
formed the writer that this pendulum had 
been made by his brother upwards of thirty 
years ago, just after he had served his time 
to Mr. Chandler, then of King Street, Seven 
Dials, (whom he afterwards succeeded in 
his business); and that it was made by di- 
rection of Mr. Chandler, who, as fer as h* 
knew, was the inventor of it: and in corro- 
boration of this assertion, Mr. Hanrpson, 
working clock-maker, 22, Greek Street, 
Soho, declares, that he made several pen- 
dulums of the same construction for Mr. 
Brown, upwards of seven years ago. Thia 
tubular pendulum, which at present we 
nmst attribute to the ingenuity of Mr. 
Chandler, is composed of two tubes and » 
P 2 
