640 BALA 
I have in equal 'balance )\ift\y weigh’d 
What wrong our arms may do, what wrongs we fuffer: 
Griefs heavier than our offences. Shakefpearr, 
The a£t of comparing two thing?, as by the balance.— 
Comfort arifes not from others being miferable, but from 
this inference upon the balance, tlrat we fuffer only the 
lot of nature. DEf range .—The overplus of weight; that 
quantity by. which,, of two things weighed together, one 
exceeds the other. That which is wanting to make two 
parts of an account even; as, He ffate'd the account with 
his correfpondent, and paid the balance. Equipoife; as 
balance of power.—A balance of power, either without or 
within a (fate,, is beft conceived by confidering what the 
natureof a balance is. It fuppofes three things; firft, the 
part which is held, together with the hand that holds it; 
and then the two fcales, with whatever is weighed therein. 
Swift. 
Love, hope, and joy, fair pleafure's fmiling train; 
Hate, fear, and grief, the family of pain ; 
Thefe mix’d with art, and to due bounds confin’d, 
Make and* maintain the balance of the mind. Pope. 
In aflronomy, one of the twelve figns of the zodiac, com¬ 
monly called Libra : 
Or wilt thou warm our fummers with thy rays* 
And feated near the balance poife the days ? Dry dm. 
Balance, in mechanics, one of the fix fimple powers, 
chiefly ufed for determining the equality or difference of 
weight in heavy bodies, and confequently their maffcs-ar 
quantities of matter. The balance is-of two kinds, the 
e««m‘ and modern-. The-ancient or Roman, called aifo 
Jlatera Rumana , or fleelyard , confifts of a lever or beam, 
moveable on a centre, and fufpended near one of its ex¬ 
tremities. The bodies to be weighed are fufpended from 
the fhorter end, and their weight is fhewn by the divilion 
marked on the beam, where the power, orconffant weight, 
which is moveable along the lever, keeps the fleelyard in 
equilibrio. This balance is ftHl in common ufe for weigh¬ 
ing heavy bodies. The modern balance, now commonly 
ufed, cortfifts-of a lover or beam fufpended exaflly in the 
middle, and having fcales fufpended from the two extre- 
mitie., to receive the weights-to be weighed. In either 
cafe the lever is called th tjugum or beam, and its two halves 
on each fide the axis, the brachia or arms ; aifo the line on 
which the beam turns-, or which divides it in two, is call¬ 
ed the axis ; and, when confidered with regard to the length 
of the brachia, is elteemed only a point, and called the cen¬ 
tre of the. balance, or centre of ■motion: the extremities, 
where the weights are applied, are the points of application 
or ffpenfon ; the handle by which the balance is held, or 
by which the whole apparatus is fufpended, is called tru- 
tina; and the (lender part perpendicular to the beam, by 
which is determined either the equilibrium or preponde- 
rancy of bodies, is called the tongue oj the balance. From 
thefe defcriptions we eafily gather the charadferiftic dif- 
tinfftion between the Roman balance and the common one, 
viz. that, in-the Roman balance, there is one conflant 
weight ufed as a counterpoife, the point where it is-Lvf- 
pended being varied ; but, on the contrary, in the common 
balance, or fcales, the points of fufpenfion remain the 
fame, and the counterpoife is varied. The principle of 
both of them may be eafily underftood from the general 
properties of the Lever, which fee. 
The beam of the balance is-a lever; but, inftead of reft- 
mg on a fulcrum, it is fufpended by a handle, &c. fatten¬ 
ed to its centre of motion; and hence the mechanifm of 
the balance depends on the fame theorems as that of the 
lever. Confequently, as the diftance between the centre 
of motion and the place of the unknown, weight, is to the 
diftance between the fame centre and the place of the 
known weight, fo is the latter weight to the former. So 
that the unknown--weight is difcovered by means of the 
known one, and their diftances from the common centre 
<af motion, viz. if the diftances-from the centre be equal, 
N C E. 
then the two weights will be equal aifo, as in the commcrs 
balance; but, if the diftances be unequal, then the weights 
aifo will be unequal, and in the very fame proportion, al¬ 
ternately, the lei's weight having fo much-the greater dif¬ 
tance, as in the fleelyard. In the common balance , or fcales^ 
the two brachia or arms fliould be exadly equal in length, 
and in weight aifo when their fcales are fixed on their 
ends; the beam fliould hang exadtly level or horizontal in 
the cafe of an equipoife; and for this purpofe the centre 
of gravity of the whole fhould fall a little below the cen¬ 
tre of motion, and but little, that the balance be fufti- 
ciently fenlible to the leafc variation of weight: the fric¬ 
tion on the centre fliould aifo he as fmall as pofiible. 
To conflruEb the Steelyard. Having made-a proper bar c-f 
fteel, as A B, in the figure, tapering at the longer end, and 
very ftrong at the other, fufpend it by a- centre C, nertr 
the fhorter or thicker end,, fo that it may exactly balance 
weight backwards and forwards upon the longer arm, till 
it be juft in equilibrio with the former, and there make a 
notch and number i; for-the place of one pound-: take oft 
the lib. and hang a two-pound-weight in its- ftead at the 
fhorter arm ; then Hide the conftant weight back on the 
longer arm, till the whole come again into equilibrio, ma¬ 
king a notch at the place of the conflant'weight and the 
number- z, for the place of two pound. Proceed in the 
fame manner for all other weights, 3, 4, 5, See. as aifo for 
the intermediate halves and quarters, &c..i£ it be necefJa- 
ry; always fnfpending the variable weights at the end of 
the fhorter arm, fhifting the conftant weight fo as to ba¬ 
lance them, and marking and numbering the places on the 
longer arm where the conftant weight always makes a coun¬ 
terpoife. The ufe of the fleelyard is hence very evident: 
the thing whofe weight is required being fufpended by>a 
hook at the fhort end, movethe conflant weight backwards 
and forwards on the longer arm, till the beam is balanced 
horizontally: then look what notch the conftant weight is 
placed at, and its number will fliew the weight of the bo¬ 
dy required. D C is the handle and tongue ; F the cen¬ 
tre of -motion ; EG afcale fometimes hung on at the end 
by the hook H. 
The deceitful Balance. This, operates in the - fame man¬ 
ner as the fleelyard, and cheats or deceives by having one 
arm a little longer than the other; though the deception 
is net perceived; becaufe the fhorter arm is made fomewhat 
heavier, fa as to compenfate for its fhortnefs, by which 
means the beam of the balance,, when no weights are in 
the fcales, hangs horizontal in- equilibrio. The confe- 
quence of this conftrudtion is,, that any commodity put m 
the fcale of the longer arm, requires a greater weight in 
the other fcale to balance it; and fo the body is faliaci- 
oufly accounted heavier titan it really is. But the trick 
will eafily be detected by. making the body and the weight 
change places, removing them to the oppofite fcales, when 
the weight will immedia|bly be fecn to preponderate. 
The bent-lever Balance is aifo an infh ument which ope¬ 
rates by a fixed weight, as at C, in .the following figure,; 
which 
