HOROLOGY. 
falls back to its position against the adjust- 
ing screw, F ; and the pallet, by receiving 
or intercepting the next tooth, stops the mo- 
tion of the escape wheel. When the balance 
returns from d to e, the unlocking pallet 
acts again on the extremity of the dis- 
charging spring, but, this being very deli- 
cate, gives way without disturbing the de- 
tent or locking spring ; and the balance, 
after suffering a trifling degree of resistance 
by that contact, continues its free vibra- 
tions. At the next vibration, the unlock- 
ing takes place ; and the action of the 
escapement proceeds successively, as ex- 
plained before. 
The detached escapement used by Mr. 
Earnshaw is represented in fig. 6, which is 
taken from his statement presented to the 
board of longitude. This escapement is 
similar to that of Arnold’s, already describ- 
ed, except in small variations, which will be 
easily perceived, on a comparison of the 
two figures. It is besides asserted, and it 
appears probable from every circumstance < 
relative to these constructions, that the late 
Mr. Arnold had made use. of this form of es- 
capement long before Mr. Earnshaw, but 
that he laid it aside, in order to adopt the 
escapement with cycloidal teeth, which 
he esteemed far preferable. In the es- 
capement we are now considering, the 
escape wheel is shaped as appears in the 
figure ; and, on the inspection of this re- 
presentation, it will be easily observed, 
that the teeth presenting a right line, and 
escaping by a sharp point, their action can- 
not be so smooth, and the wear of the whole 
must be greater, than in the construction 
with protuberant cycloidal teeth. The de- 
tent is of the same kind as the other, and 
only differs from it, in being stopped by the 
inside of the head of the adjusting screw, 
instead of the extremity of the screw itself, 
and unlocking outwards, and not towards 
the. centre. 
The two constructions, which may be 
considered as the same, differ from the 
French detached escapements, such as 
those of F. Berthoud, which we have alrea- 
dy explained, in the detent. In the new 
detent, the pivots are abolished, and the 
centre of motion is established in the lock- 
ing piece itself ; which, for that purpose, 
is made flexible near the extremity by 
which it is fixed. The elasticity of the de- 
tent, or locking piece, supplies also the 
office of a strait auxiliary spring, placed be- 
hind the lever of the detent, or a spiral spring, 
•which has been sometimes applied to the axis 
of the pivots, to keep the detent in the pro- 
per situation. 
The pivots of the old detent are so 
slender, that its performance cannot be 
supposed subject to any considerable de- 
gree of friction ; and watches, with that 
kind of detent, have been known to go very 
well. Some able artists, upon that ac- 
count, think, tliat the. new detent is only 
preferable to the other, because it saves 
work, and is less expensive ; but while the 
spring detent is allowed to perform as well, 
if not better, than the detent with pivots, 
which its universal use in this country seems 
to prove, that property, combined with the 
economy in the manufactory, must secure 
to the mechanism in question, the character 
of an improvement in the construction of 
time-keepers. 
To whom are we indebted for the inven- 
tion of the spring detent ? The general 
opinion attributes it to the late Mr. Arnold ; 
and we do not see any reason of sufficient 
weight to refuse him that merit. Mr. Earn- 
shaw has claimed it in his own favour ; but 
Mr. Arnold’s labours have, at least, the ad- 
vantage of priority ; and the strength of 
this advantage, not having been done away 
by any proofs, which in our opinion can be 
esteemed satisfactory, must decide our 
judgment in the present case, as in the like 
controversies upon other points, which have 
been considered in the course of this in- 
quiry. The contrivance of the locking 
spring, or spring detent, therefore, appears 
to ns to be due to the late Mr. Arnold. 
With regard to this mechanism, it is also 
worthy of remark, tliat the invention is en- 
tirely English, not a single passage existing 
in the writings of the French authors, by 
which any one of them might claim it with 
reason, or even plausibility. The first men- 
tion of any thing like the locking spring, to 
be found in foreign publications, is the 
detent without pivots, given by F. Ber- 
thoud in his “ Supplement au Traite des 
Horloges Marines but that book was 
published in 1787, that is five years after 
Mr. Arnold had taken out his patent, and 
when many watches upon that construc- 
tion had been in circulation. We cannot, 
therefore, allow him the credit of this 
thought ; nor do we find that other French 
artists have availed themselves of that 
hint, to carry the spring detent to the 
great degree of simplicity which it has at- 
tained in this country. 
A little after the invention of the detach- 
ed escapement, the isochronism of the vi- 
