* H ORO 
and the fpring will have more play. Thus the effect of 
heat, which tends to make the balance perform flower vi¬ 
brations, will be compenfated by the fpring becoming more 
confined between the pins, which induces quicker vibra¬ 
tions ; and the contrary. This Ample compenfation is 
the invention of Monf. Breguet. 
The following compenfation is the invention of Mr. 
Urbain Jurgenfon, who publilhed at Copenhagen, fo lately 
as the year 1805, Principes generaux de l’exa&e Mefure 
du Terns par les Horloges. The principle of this com¬ 
penfation is to render the fpiral fpring longer or fliorter 
as required, inftead of giving it more or lets play between 
the pins. A a, fig. 43, is the curb; bbc in a lamina com- 
pofed of fteel and brafs; this is fixed to the arm of the 
curb by a fcrew at d, and the other extremity, c, carries 
the two pins between which the outer coil of the fpiral 
ipring acfts. The part d of the lamina is fo fixed that the 
whole of this compenfator lies free underneath the curb. 
Now to (how the aftion of this compenfator, A, fig. 44, is 
an under view of the cock; the outer part of the fpring 
runs between the pins at f, and is pinned into the ftud G. 
The compenfator is fo fixed to the arm F of the curb, 
that the part /'has a free motion as influenced by heat or 
cold. The interior part of this compenfator being of 
brafs, heat will make the part f which carries the pins, 
move towards c, upon the principles before explained. 
The acting-part of the fpring will thereby become fhorter, 
confequently (tronger, and produce quicker vibrations, 
fo that the effeft of heat, which is to produce flow vibra¬ 
tions, is thus counteracted, or compenfated , and that more 
or lels according to the dimenfions of the compenfator 
and the length of the fpring. When cold acts upon the 
compenfator, it caules the end carrying the pins to recede- 
towards d : this makes the aftive part of the fpiral longer, 
confequently weaker; and thus the effect of cold, which 
tends to produce quick vibrations, is compenlated. This 
compenfator is fo contrived, that the arcs of the motion 
of the end f by the efteht of heat and cold are concentric 
with the centre of the fpring ; and, during the compen- 
lation, they follow the circular line of the outer coil of 
the fpring ; and, if we fuppofe this fpring of equal thick- 
nefs throughout, the compenfation mud be in proportion 
to the variation of heat or cold ; fo that this may be con¬ 
sidered as a very correct fpecies of compenfation. The 
inventor fays he has ufed this compenfator only for 
watches of a certain depth or thicknefs ; for thole of the 
flat kind, he recommends M. Breguet’s compenfator, be¬ 
fore defcribed. 
We need not at prefent notice any other compenfa- 
tions as applied to the fpring, becaufe, after all, the molt 
perfefl compenfations mull: be l’uch as are applied to the ba¬ 
lance itfelf. Yet many capital artifts have, even in longi¬ 
tude-watches, applied the compenfation to the fpring; and 
Air. Hardy has lately produced two compenfations of this 
kind ; for which he obtained a filver medal from the So¬ 
ciety of Arts in May 1807. Monf. F. Berthoud has de¬ 
fcribed at great length his modes of compenfation at the 
fpiral in his Traite des Horloges marines; and Mr. Mudge, 
in his Defcription of a Time-keeper, Lond. 1799, gives us 
the mode of compenfation at the fpiral fpring as applied 
by his father, a molt ingenious watch-maker. But this 
method is now moftly abandoned ; and Berthoud himlelf 
afterwards made leveral marine watches with the com¬ 
penfation acting on the balance itfelf. Mr. Mudge, how¬ 
ever, never changed his mode ; and to this fome are in¬ 
clined to attribute that his machines, in other refpefts fo 
excellently formed, have not had all the fuccefs that 
might have been expedled. 
The principle of a compenfation applied to the balance is 
very Ample, though very ingenious. Heat, which pro¬ 
duces flower vibrations, does at the fame time, by means 
of the compenfation, make the diameter of the balance 
lefs, fo that the centre of ofcillation is brought nearer the 
centre of motion ; and thus the effeft of heat is compen¬ 
lated ; and fo, on the contrary, of cold. 
Vol.X. No. 663. 
LOGY, 317 
There are various conltruftions of compenfation-ba- 
lances ; but the general principle is, that they are com- 
poled of two different metals, which poflefs different de¬ 
grees of expanfibility, as brafs and fteel for inflance ; of 
which two metals it has been oblerved, that the increafe 
of dimenfions by expansion, in like elevations of tempe¬ 
rature, is nearly as 8 to 5. One of the moft approved 
conftruftions of an expansion balance, is exhibited at 
fig-45> and is thus defcribed by Mr. Nicholfon: The 
outer part of the rim is brafs, and the inner fteel. After 
this compound rim is brought to its figure by turning, it 
is cut through in three places, A, B, C, which lets one 
end of each third part of the periphery at liberty to move 
outwards, when the temperature is diminiflied, or inwards 
when it is increafed. D, E, F, are three fimilar and equal 
mafles of metal, fitted upon the circular bars in a proper 
manner to admit of their being fixed at any required difi- 
tance from the extremity, where the motion is moft con- 
fiderable. G, H, I, are three ferews, the heads of which 
may be let nearer to, or further from, the centre, and 
ferve as weights to effeft the adjuftments for pofition and 
rate. The peculiar advantage of this balance may be ex¬ 
plained as follows: When an increafe of heat diminilhes 
the elaftic force of the fpring K, the outer brafs rim be¬ 
ing lengthened more than the fteel, mult throw the weights 
D, E, F, nearer to the axis, and diminifli the effefl of the 
inertia of the balance, which confequently is as fpeedily 
carried through its vibrations as before. And on the con¬ 
trary, when cold weather adds to the elaftic force of the 
fpring, the fame weights are alfo thrown further out, and 
prevent the acceleration which W'ould have followed. 
The exact adjuftment of the weights is found by trial of 
the going of the machine: if it gain by heat, the weights 
do more than compenfate, and mult be moved inwards, 
or from the extreme ends of the circular compound bars; 
but, if the gain be produced by cold, the fpring predomi¬ 
nates, and the weights will accordingly require to be let 
further out. Care mult however be taken to move the 
three weights equally, that the balance may not lofe its 
equilibrium. Mr. Arnold’s compenfation-balance is in 
two pieces only. 
We lhall have occafion to refume the fubjeft of com- 
penfation-balances when we deferibe the complete ma¬ 
chines of Mudge, Arnold, Earnlhaw, See. but in the mean 
time cannot avoid noticing a balance of a Angular form 
conftrufted by W. Hardy of Red-Lion-fquare, London, 
for which he received a premium of thirty guineas, in the 
year 1805, from the Society of Arts. Mr. Hardy’s de¬ 
fcription of his “ permanent compenfation-balance,” with 
his remarks upon other contrivances for the fame pur- 
pofe, we lhall give in his own words. 
“ We have at prefent two compenfation-balances: one 
fort confifts of feveral flips of brafs and fteel foldered or 
fluxed together, and difpofed in form of two SS’s on the 
balance ; but this is now almoft out of ufe. The other is 
a fteel balance, having a rim of brafs fluxed upon its out- 
fide, and cut open in two or three places, with Hiding 
weights placed on the rim, to increafe or diminifli the ef¬ 
fect of the balance. The nature of this balance (the ohly 
one now in ufe) is well known, as well as its defeats, 
which it is unneceflary for me to ftate at this, time. In¬ 
ftead of this uncertain way of conftructing a balance, 
which never continues long in the fame'ftate, but requires 
to be adjufted every time the watch wants cleaning, I 
have contrived a method of applying the direft expanfion 
of metals, which I find by experience to be conftant and 
permanent in its effects. 
“My balance confifts of a fteel flat bar, which forms 
its diameter. Beneath this fteel bar are two metallic rods, 
fecured at one end by a ftud, formed out of the fteel bar, 
and the other end- acting on the ftiort end of a lever, 
formed out of the other end of the fame fteel bar, being 
made to fpring at the place where the centre of the lever 
would fall; to this lever is faftened a fimall cylindrical 
Item of brafs, upon which a frnall globe of brais Hides or 
4 M ferews; 
