cylinder electrical machine
Date: circa 1766
Inventory Number: 0013
Classification: Electrical Machine
Subject:
Maker: Benjamin Martin (1704 - 1782)
Repaired by: the Reverend John Prince (1751 - 1836)
Cultural Region:
Place of Origin:
City of Use:
Dimensions:
180 x 185 x 82.2 cm (70 7/8 x 72 13/16 x 32 3/8 in.)
frame: 108 x 183 x 68.5 cm (42 1/2 x 72 1/16 x 26 15/16 in.)
wheel: 130 cm (51 3/16 in.)
Accessories: rope cord belt
glass globe
conducting pad
in folder: photographs, page containing description, history, and discussion of design, note from Ebenezer Gay regarding conservation work, excerpt from David Pingree Wheatland and I. Bernard Cohen, A Catalogue of Some Early Scientific Instruments at Harvard University (Cambridge, MA: Harvard University, 1949), woodcut with picture of instrument from B. Martin, Young Gentleman and Lady's Philosophy (1759): 139.
X-ray images of parts of the machine can be found in C1-A7.
Bibliography:
The Apparatus of Science at Harvard, 1765-1800
A Catalogue of Some Early Scientific Instruments at Harvard University
DescriptionElectrostatic generating machine mounted on a wooden frame. A red-painted, rounded glass cylinder is mounted between the spherical tops of two pillars of glass, each of which has a turned wood base. The pillars are coated in pitch, an insulating material. A third pillar has a flat surface at its top with a piece of cloth attached to it. The glass cylinder rubs against this cloth. All of this is mounted on a flat surface that is bolted into a cross beam connecting two legs. The distance between the cloth and the cylinder can be adjusted by sliding the base of the pillar through a pair of rails. The base is slotted in the middle, where a wooden screw with a turned head is used to fasten it in position. Opposite that base is another base that moves in the other direction along the rails. A short turned cylinder with a hole in its top is attached to this base.
The glass cylinder is turned by a rope connected to a large wooden drive wheel with six spokes. The wheel is turned by a brass crank with a wooden handle. The wheel axle rests in grooves carved in wooden pieces bolted to the upper beams of the frame on either side of the wheel. The axle is held in place by a pair of brass pieces screwed into the wood.
The frame resembles that of a tall, thin bed. The four spherical feet are mounted on cylindrical wheels. From the top, the frame appears to be a rectangle with the side supporting the table extended past the corner. The upper beams, which hold the drive wheel, are joined to two legs to the right and a cross beam connected the wider-spaced legs under the surface supporting the glass cylinder. The legs to the right are topped with wood spheres, while the legs supporting the table are buttressed at the top. Many of the flat surfaces of the instrument have a plate taking the form of a gold crest with bilateral symmetry across three equally spaced angles. The crank currently rests in a fitted brass notch screwed into one of the upper beams.
Two X-rays of this object's insulated posts taken by Henry Lie of the Straus Center, HU Art Museums, on 4/6/2006 are stored in C1-A7
The glass cylinder is turned by a rope connected to a large wooden drive wheel with six spokes. The wheel is turned by a brass crank with a wooden handle. The wheel axle rests in grooves carved in wooden pieces bolted to the upper beams of the frame on either side of the wheel. The axle is held in place by a pair of brass pieces screwed into the wood.
The frame resembles that of a tall, thin bed. The four spherical feet are mounted on cylindrical wheels. From the top, the frame appears to be a rectangle with the side supporting the table extended past the corner. The upper beams, which hold the drive wheel, are joined to two legs to the right and a cross beam connected the wider-spaced legs under the surface supporting the glass cylinder. The legs to the right are topped with wood spheres, while the legs supporting the table are buttressed at the top. Many of the flat surfaces of the instrument have a plate taking the form of a gold crest with bilateral symmetry across three equally spaced angles. The crank currently rests in a fitted brass notch screwed into one of the upper beams.
Two X-rays of this object's insulated posts taken by Henry Lie of the Straus Center, HU Art Museums, on 4/6/2006 are stored in C1-A7
Signedunsigned
FunctionThis is one form of electrostatic machines. Electrostatic machines were used to accumulate electric charge and create large voltages.
Contact between two different substances facilitates an electrostatic charge. Because the surfaces are usually rough, there is less contact, and therefore less charge transfer, than if the surfaces were completely smooth. Rubbing the two substances together facilitates a greater buildup of charge. Nonconductors are better at holding the charge.
The wheel is turned by a crank. The train wheel shares an axle with the glass globe, so the globe turns when the wheel turns. The glass cylinder rubs against the fabric and builds up a charge, possibly causing the globe to glow if it is evacuated.
Contact between two different substances facilitates an electrostatic charge. Because the surfaces are usually rough, there is less contact, and therefore less charge transfer, than if the surfaces were completely smooth. Rubbing the two substances together facilitates a greater buildup of charge. Nonconductors are better at holding the charge.
The wheel is turned by a crank. The train wheel shares an axle with the glass globe, so the globe turns when the wheel turns. The glass cylinder rubs against the fabric and builds up a charge, possibly causing the globe to glow if it is evacuated.
Historical AttributesBenjamin Franklin selected this large electrical machine from the shop of Benjamin Martin, Lomdon in 1766 and had it shipped to Harvard to replace apparatus lost in a fire in 1764. It originally generated electricity by rubbing a silk cushion against a glass globe. After the globe broke, the college paid the Reverend John Prince of Salem to mount a great cylinder on the frame in 1789. The uprights holding the cylinder are made of glass coated in pitch, an insulating material that Prince would have found in good supply along the Salem waterfront.
In an invoice of 1789 from Rev. Prince, there is an entry: "To mounting the great cylinder and altering the old frame for it" at a cost to the College of £4.16.0. Prince also described in a letter the way in which he altered the machine to accommodate a cylinder. A comparison of this machine and the other in the pair shows that, while the frames are substantially identical, the part containing the cylinder has been altered.
In an invoice of 1789 from Rev. Prince, there is an entry: "To mounting the great cylinder and altering the old frame for it" at a cost to the College of £4.16.0. Prince also described in a letter the way in which he altered the machine to accommodate a cylinder. A comparison of this machine and the other in the pair shows that, while the frames are substantially identical, the part containing the cylinder has been altered.
Curatorial Remarks0012 is paired with this instrument and likely purchased at the same time.
The frameworks of both large machines (0012 and 0013) are designed and constructed very much like eighteenth-century beds. Even the bolt holes are covered with similar decorative brass mounts. The wooden parts of many of these instruments--for instance, the marlboro legs and fretwork of the Pope orrery, the finials of the weights and pulley device, the cabriole legs of the large globe--bear an unmistable resemblance to furniture styles of the period. Although at this time the connection between instrument makes and cabinet makers cannot be documented, such evidence probably exists. After all, clock makers are known to have left the manufacture of cases to a cabinet maker, and instrument makers undoubtedly followed the same procedure.
The frameworks of both large machines (0012 and 0013) are designed and constructed very much like eighteenth-century beds. Even the bolt holes are covered with similar decorative brass mounts. The wooden parts of many of these instruments--for instance, the marlboro legs and fretwork of the Pope orrery, the finials of the weights and pulley device, the cabriole legs of the large globe--bear an unmistable resemblance to furniture styles of the period. Although at this time the connection between instrument makes and cabinet makers cannot be documented, such evidence probably exists. After all, clock makers are known to have left the manufacture of cases to a cabinet maker, and instrument makers undoubtedly followed the same procedure.
Primary SourcesWoodcut with picture of instrument in B. Martin, Young Gentleman and Lady's Philosophy (1759): 139.
Published ReferencesDavid Pingree Wheatland and I. Bernard Cohen, A Catalogue of Some Early Scientific Instruments at Harvard University (Cambridge, MA: Harvard University, 1949).
