HOROLOGY. 
and the friction proceeding from this cir- 
cumstance may be considered as a principal 
source of irregularity in the going of the 
■watches. Suppose, that a regulator should 
be made so perfect as to be exactly isochro- 
nal, while vibrating in a free situation : that 
advantage would be diminished or lost as 
soon as it was placed in connection with a 
train of wheels ; and the errors would be 
more or less, according to the nature and 
quantity of friction in the escapement. It 
would be, therefore, extremely useful to 
secure to the regulator a perfect liberty of 
vibration, except during the short intervals 
of time which may be necessary for the ac- 
tion of the escape wheel, to give it a new 
impulse. This ingenious idea was also started 
by P. le Roy, and carried into execution 
by the same artist, in a model which he pre- 
sented in 1748 to the Academy of Sciences 
of Paris, and is described in the collection 
of machines approyed by that society for the 
same year. Vol. vii. p. 385. 
The effect or action of Le Roy’s escape- 
ment in few vfords is this : An escape wheel 
is kept in repose by a lever detent. The 
balance unlocks the detent, and receives an 
impulse or stroke on a pallet through a part 
of every second vibration ; and during great 
part of its course it is free and detached. 
About the year 1755, according to Count 
de Bruhl, the late Mr. Thomas Mudge in- 
vented a detached escapement, and applied 
it to a watch which he made for the King 
of Spain, Ferdinand VI. This is the same 
escapement that was used by the late Josiah 
Emery in his chronometers, some of which 
have gone very well. It differs from the 
constructions which we have already ex- 
plained, both in the detent and in the com- 
munication of the impulse, which in this 
mechanism takes place at every vibration ; 
but the date will not suffer us to consider it 
as the first invention of the detached escape- 
ment. 
This justly celebrated artist afterwards 
made a chronometer, in which the vibra- 
tions of balance were kept up by secondary 
springs attached to two pallets, each of 
which was wound up by the last wheel of 
the train during the time employed by the 
balance in its vibration unconnected with 
that pallet. Though this invention is high- 
ly ingenious and was rewarded by parlia- 
ment, it is now generally considered as 
unsafe in the locking of the hooks, or detent 
parts, which terminate 'the pallets. Mr. 
Alexander Cumming executed a similar 
escapement for clocks long before Mudge 
actually carried his idea into effect, though 
it has been contended that Mudge had the 
mere notion much earlier. But Mr. Cum- 
ming, to whom our art, and the other 
branches of mechanics are highly indebt- 
ed for his labours, and his Treatise on 
Clock and Watch Making, made his detents 
separate from his pallets, and by that 
means avoided the chief defect of the con- 
struction afterwards adopted by Mudge. 
Our limits will not, however, allow us to 
pursue these and other improvements 
and variations, adopted by our own and by 
foreign artists. 
We must confine ourselves /to the con- 
structions used at present, by the English 
watchmakers ; and shall begin with that of 
the late Mr. Arnold, as describee) in his 
statement, presented by his son to the board 
of longitude. 
The teeth of the escape wheel (fig. 5.) 
are of a cycloidal shape, in the face 
part, which is intended for action, the sec- 
tion of which, with those of the two other 
sides, form a sort of mixed triangle. B B d 
represents the detent, which is formed of a 
flexible piece or spring, bending between C 
and N ; and in the part N Bi, which is 
stronger than the other, is fixed the locking 
pallet, a, opposite an adjusting screw F. 
The pallet, projecting below the spring de- 
tent, locks upon the interior angle of the 
tooth ; suspending the motion of the escape 
wheel, and leaving the balance to vibrate 
free, as pointed out in the preceding es- 
capements. YThe action of the spring de- 
tent (for the joint of the detent is itself a 
spring) presses the locking pallet against the 
screw, F, except at the time of u-nlocking 
the wheel. A very delicate spring, N e, 
called the discharging, or unlocking spring 
(and also the tender spring), is attached by 
one end, N, to the spring detent, C B N B a ; 
and, passing under the adjusting screw, F, 
extends a little beyond the extremity, d, 
of the detent itself. HHH is a circular 
piece attached to the axis of the balance, 
and, n, the discharging pallet. This pallet, 
when the balance is in motion from e to d, 
presses against the end of the discharging 
spring, n e ; and, carrying it together with 
the locking spring, B B d, disengages the 
locking piece, a, out of the internal angle of 
the tooth, with which it was in contact ; and 
the escape wheel then communicates a new 
power to the balance, by its impulse on a 
pallet, m, which is fixed, or set, in the aper- 
ture of the circu’ar piece. As soon as this 
is done, the spring detent, or locking spring, 
