| Title: | Compound backfalls |
| Original Title: | Bascules brisées de l'orgue |
| Volume and Page: | Vol. 2 (1752), pp. 115–116 |
| Author: | Unknown |
| Translator: | Charles Ferguson [Colby College, Emeritus] |
| 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.did2222.0004.014 |
| Citation (MLA): | "Compound backfalls." The Encyclopedia of Diderot & d'Alembert Collaborative Translation Project. Translated by Charles Ferguson. Ann Arbor: Michigan Publishing, University of Michigan Library, 2020. Web. [fill in today's date in the form 18 Apr. 2009 and remove square brackets]. <http://hdl.handle.net/2027/spo.did2222.0004.014>. Trans. of "Bascules brisées de l'orgue," Encyclopédie ou Dictionnaire raisonné des sciences, des arts et des métiers, vol. 2. Paris, 1752. |
| Citation (Chicago): | "Compound backfalls." The Encyclopedia of Diderot & d'Alembert Collaborative Translation Project. Translated by Charles Ferguson. Ann Arbor: Michigan Publishing, University of Michigan Library, 2020. http://hdl.handle.net/2027/spo.did2222.0004.014 (accessed [fill in today's date in the form April 18, 2009 and remove square brackets]). Originally published as "Bascules brisées de l'orgue," Encyclopédie ou Dictionnaire raisonné des sciences, des arts et des métiers, 2:115–116 (Paris, 1752). |
Compound backfalls in the organ, shown in [Plate VI] fig. 26, consist of two backfalls, CH, HD, connected by rabbets of half their thickness, as seen at H; they are mounted on frame AB, to which two wooden rails, E [F] [1], are joined with dovetails and set with pins that fit into the middle of the backfalls, acting as fulcrums with balance rails E [and F]. In the middle of the frame, where the two backfalls meet, there are two strips or bars, HG; the lower one, H, is fitted with iron pins, between which the backfalls can move. This pinned bar is called the guide rail; opposite and above it is another bar, G, whose function is to keep the backfalls from moving beyond the guide pins. The inverted balance rail, K, has the same function: it keeps backfalls HD from moving beyond the pins on rail E opposite. At each end of the backfalls, wire rings are attached: those on part C must be underneath, to connect with trackers CL going down from the keyboard to the backfall; those on part D must be on top, to connect with tracker DM, going up from the windchest to the backfall.
Compound backfalls are a sort of rollerboard (See Rollerboard), for they converge towards the trackers from the keyboard, where they have the same span as the keys they are connected to vertically. Towards the windchest, they diverge and have the same span as the pallets to which they are connected by means of trackers DM and purses. See Purse and Windchest.
When a key is depressed, tracker CL connected to it pulls down end C of backfall CH , which rocks at point E . End C cannot lower without raising the other end, H , but this part is connected to one end of the other backfall , HD ; consequently, it must raise it towards rail G , which must pull backfall HD down, and with it tracker DM , connected to the corresponding purse and pallet in the windchest, which opens. When the key is released, the spring holding the pallet on the channel will pull up on tracker MD , raising end D of the backfall and consequently lowering the other end, H ; because it rests on the end of the other backfall , it will lower it and consequently raise the other end, C , which will pull up tracker CL and raise the manual key connected to it.
1. The Plate labels the second balance rail “F” (Translator’s note).