Polygraph (duplicating device)
Encyclopedia
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
in 1803, it was most famously used by the third U.S. president, Thomas Jefferson
, who acquired his first polygraph in 1804, later suggesting improvements to Charles Willson Peale
, owner of the American rights. As a prolific letter writer, the preservation of Jefferson's copies have offered historians extensive insights into Jefferson's viewpoints and actions.
Jefferson called the polygraph "the finest invention of the present age". A description of Jefferson's office routine in his own words may be read here.
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.
The quality of the copy made by a machine in good condition is so fine that it is considered by some 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.
Mechanisms of this type are more generally known as pantograph
s, which include simple devices for making copies at various enlargements or reductions by tracing over a drawing.
Note: For a better image of the device than is provided above see. For a Quicktime animation see.
For an image of a later portable version see.
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.
In addition, a vertical suspension spring balances the weight of the moving parts.
A simple pantograph is used to translate the planar motion of one pen to the other. The pantograph consists of two complete variable parallelogram
s.
The base parallelogram is attached to two fixed pivot points at the far side of the base plate. The pivoting arms are supported at their mid-points by wheels which rest on the base and this part remains in a plane parallel to the base.
The extension parallelogram is attached to the base parallelogram by pivots that allow the pen-side edge to be lifted away from the base.
Some United States locations:
Patented by John Isaac Hawkins
John Isaac Hawkins
John Isaac Hawkins was an inventor who practiced civil engineering.He was known as the co-inventor of the ever-pointed pencil, an early mechanical pencil, and of the upright piano.-Life:...
in 1803, it was most famously used by the third U.S. president, Thomas Jefferson
Thomas Jefferson
Thomas Jefferson was the principal author of the United States Declaration of Independence and the Statute of Virginia for Religious Freedom , the third President of the United States and founder of the University of Virginia...
, who acquired his first polygraph in 1804, later suggesting improvements to Charles Willson Peale
Charles Willson Peale
Charles Willson Peale was an American painter, soldier and naturalist. He is best remembered for his portrait paintings of leading figures of the American Revolution, as well as establishing one of the first museums....
, owner of the American rights. As a prolific letter writer, the preservation of Jefferson's copies have offered historians extensive insights into Jefferson's viewpoints and actions.
Jefferson called the polygraph "the finest invention of the present age". A description of Jefferson's office routine in his own words may be read here.
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.
The quality of the copy made by a machine in good condition is so fine that it is considered by some 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.
Mechanisms of this type are more generally known as pantograph
Pantograph
A pantograph is a mechanical linkage connected in a special manner based on parallelograms so that the movement of one pen, in tracing an image, produces identical movements in a second pen...
s, which include simple devices for making copies at various enlargements or reductions by tracing over a drawing.
Description of the device
- Note: The original U.S. patent documents are not available, having been destroyed in an 1836 patent office fire, but fundamentals of the design are readily revealed by careful examination of surviving examples and related images. Part names used here may not correspond to those used originally. Other patent documents may be available in England and France.
Note: For a better image of the device than is provided above see. For a Quicktime animation see.
For an image of a later portable version see.
Platform
The platform forms both a writing surface (in part) and a base and reference plane for the moving and other stationary parts. 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.Bridge
Also known as a "gallows frame", the bridge spans the platform. 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.
Inkwells
Inkwells 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 parts
The device consists of two pens transmitting motion in five degrees of freedom through four interlinked mechanisms:- A horizontal pantograph maintains identical planar (X and Y axis) movement, with two degrees of freedom
- An angled pantograph descending from the bridge maintains identical vertical (Z axis) movement
- A torsion beam maintains identical pen fore-and-aft tilt
- A parallel linkage maintains identical pen side-to-side tilt
In addition, a vertical suspension spring balances the weight of the moving parts.
Planar pantograph
The 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 parallelogram
Parallelogram
In Euclidean geometry, a parallelogram is a convex quadrilateral with two pairs of parallel sides. The opposite or facing sides of a parallelogram are of equal length and the opposite angles of a parallelogram are of equal measure...
s.
Base parallelogram
The base parallelogram is attached to two fixed pivot points at the far side of the base plate. The pivoting arms are supported at their mid-points by wheels which rest on the base and this part remains in a plane parallel to the base.
Extension parallelogram
The extension parallelogram is attached to the base parallelogram by pivots that allow the pen-side edge to be lifted away from the base.
Decending pantograph
A second pair of parallelogram links maintains vertical correspondence between the two pens. 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 transfer
The combination of forces between the horizontal and vertical enables the pen lift of the principle pen grasped by the user from the paper to be transferred to the copying pen.Pen mounts
Each pen is mounted in such a way that it allows the pen to be used at various angles, necessary to allow a normal writing style. The pens are offset from their pivots by a short stem that projects at right angles from below the midpoint of the pen, allowing the pen to be grasped in whatever way is usual to the user.Pen tilt (fore and aft)
A torsion beam joins the pen mounts to maintain correspondence of tilt with respect to the direction away from the user.Pen tilt (side-to-side)
A parallel linkage maintains correspondence of tilt with respect to a direction parallel to the front face of the device.Suspension beam and spring
At the center of the bridge a beam projects horizontally toward the user, from which a vertical suspension spring balances most of the weight of the moving parts so that the user is neither fatigued by using the device nor is required to adjust their writing style.Viewing in museums
Original polygraphs may be viewed at a number of locations around the world.Some United States locations:
- Montecello, Jefferson's estate in Virginia
- Smithsonian National Museum of American HistoryNational Museum of American HistoryThe National Museum of American History: Kenneth E. Behring Center collects, preserves and displays the heritage of the United States in the areas of social, political, cultural, scientific and military history. Among the items on display are the original Star-Spangled Banner and Archie Bunker's...
, Washington, D. C.
A modern version
The Griffin Discovery Room at Montecello contains a simplified and durable version, intended for use by children. An image of this version in use may be seen here.http://www.monticello.org/featured/8griffin_room.htmlExternal links
For a general search of the Montechello website related to the polygraph, click here.Further reading
- Bedini, Silvio A. (1984). Thomas Jefferson and His Copying Machines. Charlottesville: University Press of Virginia. ISBN 9780813910253
External links
- Polygraph article at Jefferson Encyclopedia (Monticello.org)
- Jefferson and the Polygraph report (Monticello.org)
- The Letters of Thomas Jefferson: 1743–1826 (partial index)
- Material Rhetoric: Jeffersonian Democracy and the Technology of the Public Record Including quotations from Jefferson about the polygraph and the connection between Jefferson's philosophies and the technologies he employed (Texas Tech University, Department of English)
- A Modern Monticello Do we really need interactive exhibits to bring Jefferson to life? Yes, we do. By Anne Applebaum (Slate.MSN.com)
- Portable version of the Polygraph Image at Make.com
- Monticello's Makeover Describes public hands-on access to a replica Polygraph.
