Atwood's Machine

An Atwood’s machine with magnetic drop mechanism and pendulum timer. Inscribed on clock: “Presented to Yale College by Mt. Richard S. Fellows.” “Secretan sucr. de Lerebours, Paris.” YPM catalog no. 1.370

The Atwood’s Machine, designed in 1770 by the Cambridge mathematician George Atwood, was used to study motion and acceleration. Sir Issac Newton, over 50 years earlier, had established his three laws of motion, but Atwood complained that in “books of mechanics no account is found of methods by which the principles of motion may be subjected to decisive and satisfactory trials.” Designed to control the effects of imposing factors such as wheel friction, Atwood’s machine could demonstrate Newton’s theories by modifying and measuring velocity, accelerating force and distance.

The machine has 2 equal weights A and B, suspended by a thread over a wheel. Weight C, released by a pendulum clock at a precise minute, provides the impetus for B to fall. To measure the velocity of B against A, a brass ring captures weight C once weight B has reached a desired velocity. The ring allows B to fall through unhindered. One-inch increments on the shaft measure distance. The release mechanism, the brass ring and the mechanism to stop the falling weight are all adjustable.

This Atwood’s machine was donated to Yale by Richard S Fellows. Unfortunately, neither the instrument nor the donation plaque is dated. But, the printed inscription on the clock face (see above) clearly indicates that this particular machine was made in France by Lerebours et Secretan. It is listed for 1,000 francs in their 1853 Catalogue et Prix des Instruments D’optique, de Physique, de Chime, de Mathematiques, d’Astronomie et de Marine.

Elias Loomis, Professor of Natural Philosophy and Astronomy at Yale College, describes the mechanisms of this machine in his Elements of Natural Philosophy (1860) and uses the same picture as featured in the Lerebours et Secretan Catalogue. Professor Derek J. de Solla Price, in his description of the machine, records the weight drop release mechanism to be “magnetic,” which is consistent with other descriptions of 19th century Atwood machines. Loomis, in contrast, describes the release of the weight as initiated by a lever that is displaced by a “wheel” with a “protruding shoulder.” The 1853 Catalogue does not mention the magnetic release mechanism. Future investigations into the origins of the machine and its mechanisms could resolve the inconsistencies in the record and perhaps provide a date of manufacture.

Sources
Bud, R., ed., Instruments of Science: An Historic Encyclopedia, 1998, pp.36–38.

Lerebours et Secretan, Catalogue et Prix des Instruments D’optique, de Physique, de Chime, de Mathematiques, d’Astronomie et de Marine, 1853, p. 141.

Loomis, E., Elements of Natural Philosophy Designed for Academies and High Schools, 1860, pp. 25–26.

Price Catalogue # 637, Atwood’s machine with magnetic drop mechanism, pendulum timer. Wooden supporting pole and base brass pulley, mechanism, and fittings.