Balance
2 of the 7 encyclopedias on this shelf carry an entry for Balance. Both are reproduced below, so you can see where they agree and where they differ.
American Watchmaker and Jeweler (1892)
The wheel in a watch, clock or chronometer which is kept in vibration by means of the escapement and which regulates the motion of the train. The size and weight of a balance are important factors in the time-keeping qualities of a watch, although the dimensions of a balance are not criteria of the time in which the balance will vibrate. The balance is to a pocket time-piece what the pendulum is to a clock; although there are two essential points of difference. The time of vibration of a pendulum is unaffected by its mass, because every increase in that direction carries with it a proportional influence of gravity; but if we add to the mass of the balance we add nothing to the strength of the hairspring, but add to its load and therefore the vibrations become slower. Again, a pendulum of a given length, as long as it is kept at the same distance from the earth's center, will vibrate in the same time because the gravity is always the same; but the irregularity in the force of the hairspring produces a like result in the vibration of the balance. Britten says there are three factors upon which the time of the vibration of the balance depends: 1. The weight, or rather the mass, of the balance. (The mass of a body is the amount of matter contained in that body, and is the same irrespective of the distance of the body from the center of the earth. But its weight, which is mass X gravity, varies in different latitudes.) 2. The distance of its center of gyration from the center of motion, or to speak roughly, the diameter of the balance. From these two factors the moment of inertia may be deducted. 3. The strength of the hair-spring, or more strictly its power to resist change of form. Balances are of two kinds, known as plain or uncut, and cut or compensation. The plain balance is only used in this country on the very cheapest variety of movements. The compensation balance is used on the better grades of watches. The plain balance is usually made of brass or steel, while the compensation balance is made of steel and brass combined. Some English makers use gold for plain balances, it being denser than steel and not liable to rust or become magnetized. The process of compensation balance making as carried on in our American factories is as follows: A steel disc, one eighth of an inch thick and five-eighths of an inch in diameter, is first punched from a sheet of metal. It is then centered and partially drilled through, the indentation serving as a guide in the operation to follow. A capsule of pure copper three-fourths of an inch in diameter is then made, and in the center of this capsule the steel disc is lightly secured. A ring of brass one-sixteenth of an inch in thickness is then made and placed between the copper capsule and the blank, and the whole is fused together. It is then faced upon both sides. It is then placed in a lathe and cut away in the center until a ring is formed of steel, which is lined or framed with brass. It then goes into the press, where two crescents are cut from it, leaving only the inner lining of the ring and the cross bar of steel. The burr is then removed and the balance is ready to be drilled and tapped for the balance screws. This method of making balances is known as the "capsule method."
Collier's New Encyclopedia (1921)
an instrument for determining the relative weights or masses of bodies. It consists of a beam with its fulcrum in the middle, and its arms precisely equal. From the extremities of the arms are suspended two scales, the one to receive the object to be weighed, and the other the counterpoise. A false balance of this type is one in which the arms are unequal in length. As the balance is really a lever, it is evident that a smaller weight than that in the scale will put the beam into equilibrium. The fraud may at once be detected by putting the article to be weighed into the scale containing the weight, and vice versa. Hydrostatic balance: A balance designed for the weighing of bodies in water, with the view of ascertaining their specific gravity. A Roman balance, the same as the steel yard. Of this type the Chinese, the Danish or Swedish, and the bent lever balances are modifications. In mechanics and natural philosophy: Balance of torsion: An instrument invented by Coulomb for comparing the intensities of very small forces. It consists of a metallic wire suspended verti cally from a fixed point, to the lower end of which a horizontal needle is attached with a small weight designed to keep the wire stretched. The magnitude of a small force acting on the end of the needle is measured by the amount of torsion, or twisting of the wire-in other words, by the arc which the needle passes over measured from the point of repose. In horology: 1. Balance of a watch: The circular hoop or ring which takes the place of the bob of a pendulum in a clock. The action of a hair-spring causes it to vibrate. 2. Compensating balance of a chronometer: A balance, or wheel, furnished with a spiral spring, with metals of different expansibility so adjusted that, in alterations of temperature, they work against each other and render the movements of the chronometer uniform. In astronomy: A constellation, one of the signs of the zodiac, generally designated by its Latin name, Libra. In book and account keeping: The excess on the debtor or creditor side of an account, which requires to be met by an identical sum entered under some heading on the other side if an equilibrium is to be established between the two. In commercial and political economy: Balance of trade, properly an equilibrium between the value of the exports from, and the imports into, any country, but more commonly the amount required on one side or other to constitute such an equilibrium. In politics: Balance of power, such a condition of things that the power of any one state, however great, is balanced by that of the rest. BALBEC. See BAALBEK.