HOEO 
iiovpn by its ratchet, and again when it is fet high, or has 
its intensity increafed ; which alteration is equivalent to an 
addition or fubtraftion of weight in the maintaining-power 
of a clock in order to increa/e or diminilh the arc of vi¬ 
bration in a pendulum. When the chronometer is new, 
or clean if ufed fome time, the femi-arc of vibration varies 
according to cii'cumftances from iBo° to 230 0 , making in 
the whole vibration from a circle to 4.60°; but, when tire 
oil grows thick, or when dirt has obtained admifiion into 
the upper part of the train, the arc will fometimes be re¬ 
duced to 24.0 0 ; fo that, if the long and Ihort arcs were not 
performed in the lame time preci/ely, an alteration would 
take place in the rate, which might be confiderable enough 
to do away all dependence on an accurate meafurement of 
time. The balance-fpring is u/'ually made by Mr. Arnold 
of fteel wirehardened and tempered, though, he fays, that 
wire hard-rolled, or wire made of gold with a mixture of 
from one eighth to one quarter of copper, will do ; but 
the two latter are lefs permanently elaftic, and the hard- 
rolled wire will fometimes require to be tapered at that 
end which is next the balance-ftud: the belt: length of a 
balance-fpring, whith is longer in box than in pocket 
chronometers, lies between 5 and zo inches to become 
ifochrdiial ; but Mr. Arnold does not feem to apprehend 
that there are various intermediate lengths, as Mr.-Pen¬ 
nington alferts, which are equally ifochronal. In the 
box-chronometer, which has a heavier balance than the 
pocket one, and a flower train, the weight is taken from 
the fupporting pivot of the verge, by an ingenious appli¬ 
cation of the cylindrical regulatmg-fpring, thus: when the 
lpring is wound round a cylinder, to be blued, the coils 
are put contiguous, which fliape would be afterwards 
preferved, from the elaftic temper then given to It, if no 
force were to feparate them ; but, when one end of the 
lpring is attached to the verge-collet, and the other to the 
ftud, thefe oppoflte ends are forcibly removed from each 
other to Inch a diftance, that the coils are /eparated from 
contact, and the effort, exerted to bring them again into 
contact by their elafticity, lifts nearly the whole weight of 
the balance. Formerly there was a contrivance of bank¬ 
ing in Mr. Arnold’s chronometers, but the banking-pin 
or lever, rubbing between two coils of the lpring, was 
found to be injurious, and was therefore laid afide; and we 
do not learn that any other banking has been fubftituted. 
Mr. Arnold lays great ftrefs on his ftud being placed fo 
as to fix the end of his balance-fpring at half the diftance 
between the centre and circumference of the coils, fo that 
the laft coil, at each end, is made fo much fmaller than 
the relt, as prevents any protmfion of the large coils, and 
preferves the cylindrical lhape apparently unaltered by 
the action. 
We underhand, that neither of the two Arnolds ever 
placed a chronometer for trial at the royal obfervatory, for 
the exprefs purpo'fe of applying for parliamentary remu¬ 
neration ; but we have i'een, under our account of Mr. 
Mudge’s time-keeper, that Nos. 36 and 68 were tried 
againft his, and pronounced to be l'uperior, both with re- 
fpeft to their accurate going, and alio in regard to the 
fimplicity and practicability of their conftruFrion ; lb that 
1322I. were given to Mr. Arnold, fen. by the board of 
longitude at different times by way of encouragement, 
and 167SI. its completement to 3000L were given in De¬ 
cember 1805 to Mr. Arnold, jun. being at the fame time 
that 25001. were given to Mr. Earnfliavv, in addition to the 
500I. which he had previoufly received. When the quef- 
tion was difficult to decide, whether Mr. Arnold’s or Mr. 
Earnlhaw’s chronometers were molt worthy of public re¬ 
ward, the board of longitude very properly rewarded the 
labours of both thefe makers equally. But fir Jofeph 
Banks, whole oppofition to Mudge’s applications is well 
known, and who feems a greater enemy to time-keepers 
than Dr. Malkelyne, entered a proteft againft the refiolu- 
tion of the board, to which Dr. Malkelyne replied in a 
private pamphlet. 
Earnjhaw's Chronometer. —For the fame reafon that we 
Voi» X, Np. 666. 
LOGY, Sbl 
have not given the firovement find parts fcf the chronome¬ 
ter contained in the frame of Fir. Arnold, we think it 
not necefiary particularly to defcribe all the parts of Mr. 
Earn/haw’s that are common to the other modern chro¬ 
nometers., The peculiarities of the conftrucliou ale con¬ 
fined to the balance, the balance-fpring, the fcapement- 
wheel, and the acting parts of the fcapement. To theft: 
parts, therefore, we propole to confine our account. M:\ 
Earnfliavv fays, that his train is 18000 vibrations of the 
balance in an hour, which, we have feen, has always been 
the train of the other chronometer-makers, particularly 
for the pocket ones; his box pieces have 13 teeth each in 
the Icapement-wheel, and his pocket ones 15. We are 
not told what pinions are ufed in the movements; nor is 
it faid, in Mr. Earnlhaw’s account delivered to the board 
of longitude, that this is a consideration of any moment. 
Fig. 93 is a copy of Mr. Earnlhaw’s firft figure of his third 
plate, which was taken from his model laid before the 
board of longitude on June 7th 1804, at the fame time 
that Mr. Arnold’s model was produced ; the balance and 
cocks, being not neceflaiy for explaining the mode of 
action, are in our figure omitted. Mr. Earnfhaw has 
given fo minute an account of his fcapement accompany¬ 
ing the model, that we cannot defcribe it better than by 
copying his own words, which are nearly thefe: viz. 
“The fmall wheel MSK is called the large pallet; it 
is a cylindrical piece of fteel, having a notch or piece cut 
out of it at Ih r; againft the fide of this notch is a fiquare 
flat piece of ruby, or any hard ftone, hi, ground and po- 
lilhed very fmooth, and fixed faft into the pallet. The 
cylinder is fo placed, with refpeft to the balance-wheel, 
that it may rtot be more than juft ciear of two adjoining 
teeth. EF is a long thin lpring, which is made faft at 
one end, by being pinned into a ftud, G, and made to 
bear gently againft the head of an adjufting ferew, m ; the 
other end is bent a little into the form of a hook; to this 
lpring there is fixed another very /lender fpring at Y r 
which projects to a fmall diftance beyond it. This fmall 
fpring lies on the fide of the thick fpring neareft to the 
balance-wheel. The adjufting ferew, m, takes into a fmall 
brafs cock, at Va, which is ferewed faft to the upper plate 
by a ftrong ferew. Upon the fpring EF there is fixed a 
femi-cylindrical pin, which ftands up perpendicular upon 
if, and of a fufficient length to fall between the teeth of” 
the balance-wheel ABCD. This pin is called the lock¬ 
ing-pallet, and is placed on the oppofite fide of the fpring 
reprefented to view. Through the centre of the cylin¬ 
drical pallet MSK, a ftrong fteel axis paffes, called the 
verge; the pallet is made faft to this axis, which alfo 
pailes through the centre of the balance, wnd is made faft 
to it; it has two fine pivots at its extremities, upon 
which it turns very freely, between two firm fupporting 
pieces of brafs, ferewed firmly, and made as permanent 
as poflible, by fteady pins, to the principal plate. A lit¬ 
tle above the cylindrical pallet MSK is fixed a fmffll cy¬ 
lindrical piece of fteel, in, having a fmall part projecting 
out at i, through which the verge alfo paffes ; this is call¬ 
ed the lifting-pallet, (and is from j to £ the diameter of 
the large pallet;) it fixes upon the verge like a collar, 
and is made fait by a twift, fo as to be let in any pofition 
with refpedt to the large pallet MSK. The end EG of 
the long fpring EF being made very /lender, if a final} 
force be applied at the point 0 to prefs that end out from 
the wheel ABCD, it eafily yields in that direction, rurn*- 
iqg, as it were, upon a centre at G ; it is alfo made to 
Aide in a groove made in this ftud, in fuch a manner that 
the end 0 may he placed at any required diftance from- 
the centre of the verge. 
“ Having deferibed the feveral parts as they appear in 
the figure, we next come to their connection or iituation 
with refpect to each other. Let the long fpring EFbe 
fuppo/ed to be fo placed, that the end of the llender lpring 
Y i may project a little way over the point of the lifting- 
pallet in, but not fo clofe but that the point of the pallet 
mav pafs by the hooked end of the lpring E F without 
4 Y touching 
