| Title: | Chronometer |
| Original Title: | Chronometre |
| Volume and Page: | Vol. 3 (1753), p. 402 |
| Author: | Jean Baptiste Le Roy (biography) |
| Translator: | Charles Ferguson [Colby College, Emeritus] |
| Subject terms: |
Clockmaking
|
| Original Version (ARTFL): | Link |
| Rights/Permissions: |
This text is protected by copyright and may be linked to without seeking permission. Please see http://quod.lib.umich.edu/d/did/terms.html for information on reproduction. |
| URL: | http://hdl.handle.net/2027/spo.did2222.0002.911 |
| Citation (MLA): | Le Roy, Jean Baptiste. "Chronometer." The Encyclopedia of Diderot & d'Alembert Collaborative Translation Project. Translated by Charles Ferguson. Ann Arbor: Michigan Publishing, University of Michigan Library, 2013. Web. [fill in today's date in the form 18 Apr. 2009 and remove square brackets]. <http://hdl.handle.net/2027/spo.did2222.0002.911>. Trans. of "Chronometre," Encyclopédie ou Dictionnaire raisonné des sciences, des arts et des métiers, vol. 3. Paris, 1753. |
| Citation (Chicago): | Le Roy, Jean Baptiste. "Chronometer." The Encyclopedia of Diderot & d'Alembert Collaborative Translation Project. Translated by Charles Ferguson. Ann Arbor: Michigan Publishing, University of Michigan Library, 2013. http://hdl.handle.net/2027/spo.did2222.0002.911 (accessed [fill in today's date in the form April 18, 2009 and remove square brackets]). Originally published as "Chronometre," Encyclopédie ou Dictionnaire raisonné des sciences, des arts et des métiers, 3:402 (Paris, 1753). |
Chronometer. M. Graham, an excellent horologist and member of the [Royal] Society of London, gave this name to a small portable clock of his invention that counts thirds [1] and is most useful in astronomical observations; it can easily be started at the precise instant when the observation begins and stopped likewise at the instant it ends, giving the exact time of its duration.
To understand how this is accomplished, imagine a part similar to a balance wheel with three arms, having a radius a bit shorter than the pendulum of the chronometer ; one arm is on one side of the center, and the other two arms and the space or zone between them on the other side. Imagine further that this part is mounted on the back plate as follows: 1) parallel to the plate, it is fixed by its center over the suspension point of the pendulum in such a way that a line drawn from the center of the part to the middle of the zone is parallel to the vertical of the pendulum and in a plane perpendicular to the plate, imagined as passing through this vertical; 2) hinged at its center, it can be moved at will closer or farther from the plate. Imagine further that the zone has pins on the side facing the plate, set at various distances from the vertical of the pendulum so that if [the pendulum] dropped from the height of these pins, it would gain enough motion to continue moving, and the chronometer going. The arm opposite the zone extends through the case, in order that without opening it one can set the pendulum in motion; by means of this arm or tail the zone can be moved towards or away from the pendulum, thus freeing it from between the pins.
Using this instrument . The pendulum is away from the vertical and rests on one of the pins we mentioned; at the instant the observation begins, it is set going when released from the pin by means of the arm extending through the case. When the observation ends, the arm is moved in the opposite direction, and the pins encounter the pendulum, stopping it. See Balance, Pendulum, etc.
Note
1. Known in French as tierces , sixtieths of a second.