词条 | Polygraph (duplicating device) |
释义 |
A Polygraph is a device that produces a copy of a piece of writing simultaneously with the creation of the original, using pens and ink. Patented by John Isaac Hawkins on May 17, 1803,[1] it was most famously used by the third U.S. president, Thomas Jefferson, who acquired his first polygraph in 1804 and later suggested improvements to Charles Willson Peale, owner of the American rights. Because Jefferson was a prolific letter writer, the preservation of his copies have offered historians extensive insights into Jefferson's viewpoints and actions.[2] Jefferson called the polygraph "the finest invention of the present age".[3][4] A description of Jefferson's office routine in his own words may be read online.[5][6] Another American, Benjamin Henry Latrobe was the first customer of Peale's and not only introduced the device to Jefferson but was also instrumental in its improvement.[7] The quality of the copy made by a machine in good condition is so fine that it is considered by some[8] that only characteristics other than the quality of the script (e.g., having been mailed, etc.) are reliable indicators (under the assumption that the original was mailed and not the copy), although a worn or maladjusted machine will produce specific indications in the copy.[8] Mechanisms of this type are more generally known as pantographs, which include simple devices for making copies at various enlargements or reductions by tracing over a drawing. Description of the deviceSee[9] for a QuickTime animation. Stationary partsPlatformThe platform forms both a writing surface (in part) and a base and reference plane for the moving and other stationary parts.("F" on diagram) In a portable device the platform is in two parts that form the covers of the enclosure formed for transport. As suggested by Jefferson, a non-portable version uses a single board for the entire platform. BridgeAlso known as a "gallows frame", the bridge spans the platform ("A" and "B" on diagram). In the non-portable device this is mounted on posts permanently attached to the platform. In the portable version the bridge, side posts, and a bottom cross piece form the outer rim of enclosure when in the state for transportation. The bridge divides the platform into two portions, the part toward the user upon which the papers are placed (see illustration above), and the stationary part away from the user that contains a portion of the planar pantograph. The function of the bridge is to form a base for the vertical movement linkage and a support for the suspension spring support beam. InkwellsInkwells are provided beneath the bridge for each pen at corresponding locations. The dipping of the master pen will thus re-ink the slave pen. Moving partsThe device consists of two pens transmitting motion in five degrees of freedom through four interlinked mechanisms:
In addition, a vertical suspension spring balances the weight of the moving parts. Planar pantographThe range of the planar mechanism must be sufficient to encompass the papers (individually) being written upon and allow access for each pen to its respective inkwell. A simple pantograph is used to translate the planar motion of one pen to the other. The pantograph consists of two complete variable parallelograms ("d" and "e" on diagram):
Descending pantographA second pair of parallelogram links maintains vertical correspondence between the two pens ("D" and "E" on diagram). These consist of two variable parallelogram frames attached at a common edge, one of which is also attached to the bridge, while the other is attached to one of the pen supports at each corner. The projecting sides of the upper frame consist of parallel linkages. Pen lift transferThe combination of forces between the horizontal and vertical enables the pen lift of the principal pen grasped by the user from the paper to be transferred to the copying pen.
Viewing in museums{{Expand section|date=January 2011}}Original polygraphs may be viewed at a number of locations around the world. Some United States locations:
PatentThe original American patent document for the polygraph, issued to John J. Hawkins on May 17, 1803, was lost in a Patent Office fire in 1836.[1] A modern versionThe Griffin Discovery Room at Monticello contains a simplified and durable version, intended for use by children. An image of this version in use may be seen here. See also
References1. ^1 http://wiki.monticello.org/mediawiki/index.php?title=Polygraph&printable=yes 2. ^The Works of Thomas Jefferson, 12 vols. At The Online Library of Liberty (website of Liberty Fund, Inc.) 3. ^Some information and quotation from curator's card, Smithsonian Museum of American History 4. ^Letter: Thomas Jefferson to James Bowdoin, July 10, 1806, Washington – Writings of Jefferson 6:7 The full line is "I think it the finest invention of the present age and so much superior to the copying machine that the latter will never be continued a day by any one who tries the polygraph". The "copying machine" refers the copying press, which enabled a copy to be made by writing the original using special transferable inks and damp papers to receive the copies. (quoted and described in Bedini, p. 147.) 5. ^{{cite web|url=http://www.monticello.org/jefferson/dayinlife/cabinet/home.html|title=A Day in the Life of Thomas Jefferson - Thomas Jefferson's Monticello|website=www.monticello.org}} 6. ^{{cite web|url=http://www.monticello.org/jefferson/dayinlife/cabinet/home.html|title=A Day in the Life of Thomas Jefferson - Thomas Jefferson's Monticello|website=www.monticello.org}} 7. ^Bedini, Silvio A. (1984). Thomas Jefferson and His Copying Machines. Charlottesville: University Press of Virginia. {{ISBN|978-0-8139-1025-3}}, p. 53 et al. 8. ^1 Thomas Jefferson and the Polygraph (The Raab Collection, monograph concerning difficulty of authenticating originals vs. copies in Jefferson's letters: "Textual anomalies have not historically been considered as indicators") 9. ^Polygraph movie (requires an appropriate browser plug-in and browser setting) To use this animation, place the cursor on the image, click, and drag. The pens will follow your movement in the writing plane, but pen lift and the pen tilts are not demonstrated. Further reading
External links
2 : Technical drawing|Printing |
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