Barrel
3 of the 7 encyclopedias on this shelf carry an entry for Barrel. Both are reproduced below, so you can see where they agree and where they differ.
American Watchmaker and Jeweler (1892)
A cylindrical box made of brass or steel in which the mainspring of a watch or clock is confined. Barrels are of two general types, those with and those without teeth around their circumference. In fuzee watches the power is conveyed to the fuzee by means of a chain and from the fuzee to the center pinion by means of the great wheel on the fuzee. In American watches the barrel has teeth cut upon its circumference and gears directly into the center pinion. The latter type is generally known as the "going barrel." The going barrel is again divided into two types, one which has a support at both ends of the arbor and the other which is supported only at the upper end by the ratchet wheel. This latter form, which is sometimes termed the overhanging barrel, is generally found in repeaters and complicated watches, where economy of space is found desirable. This type of barrel is objectionable even in the very best makes of watches on account of the undue friction of the ratchet wheel and its liability to become out of upright by even the smallest amount of wear. Where this style of barrel is used, the objections may, to a certain extent, be overcome by the use of a large ratchet wheel and superior fitting. Of late years steel has taken the place of brass for barrels very largely, especially among American makers, but these barrels do not find favor among repairers as it is very difficult to replace the mainspring hook when broken. The barrel dates from about 1500, but is not as old as the main spring, for there are many examples still in existence of antique watches which had no barrel proper. This is illustrated by a watch, which is in the collection of Mr. Carl Marfels, of Berlin. In this specimen the mainspring is confined within the limits of four iron pins, and the motion is conveyed to the train through the medium of the staff and a great wheel.
Collier's New Encyclopedia (1921)
a word having many applications, including: I. Of anything shaped like a cask. (1) A cask; a vessel bulging in the middle, formed of staves surrounded by hoops, and with a bunghole to afford egress to the generally liquid contents. (2) The capacity of such a cask, supposing it to be of the normal magnitude. In one for holding liquids the capacity is usually from 30 to 45 gallons. II. Of anything hollow and cylindrical. The metallic tube which receives the charge in a musket or rifle. With the stock and the lock, it comprises the whole instrument. III. Of anything cylindrical, whether hollow or not. A cylinder, and especially one about which anything is wound. Technically.-I. Measures. As much as an ordinary barrel will hold. Specially: (1) Liquid measure. In this sense the several liquids have each a different capacity of barrel. A barrel of wine is 31/2 gallons; a barrel of oil averages from 50 to 53 gallons. (2) Dry measure. A barrel of flour contains 196 pounds. pounds . II. Mechanics: The cylindrical part of a pulley. III. Horology: (1) The barrel of a watch. The hollow cylinder or case in which the mainspring works. It is connected with a chain by the fusee, by the winding of which the chain is unrolled from the cylinder, with the effect of winding the mainspring. (2) The chamber of a spring balance. IV. Campanology: The sonorous portion of a bell. V. Anatomy: Barrel of the ear: A cavity behind the tympanum, covered with a fire membrane. The belly and loins of a horse or cow are technically spoken of as the barrel. VI. Nautical: (1) The main piece of a capstan. (2) The cylinder around which the tiller-ropes are wound. VII. Music: The cylinder studded with pins by which the keys of a musical instrument are moved.
Aiton's Encyclopedia (1910)
. See Cooper