Diffraction Grating
   The first practical diffraction gratings were made in 1820 by Joseph von Fraunhofer (1787-1826), a Munich optical worker. He stretched fine, parallel wires between two parallel threaded rods, and was able to resolve the sodium D lines. Since then this technique has be mainly used in the longer wavelengths of the infrared region, but I have reconstructed Fraunhofer's work with wire gratings and visible light. REF: Thomas B. Greenslade, Jr., "Wire Diffraction Gratings", Amer. J. Phys., 41, 730-731 (1973)
   The American lawyer and amateur scientist, Lewis M. Rutherfurd, developed ruling engines in the eighteen sixties and seventies that were able to rule gratings about two inches in width. These were considered remarkable for their time.

   This example of a Rutherfurd grating at the United States Military Academy at West Point is in a gutta percha case that probably originally housed a daguerreotype or ambrotype.

   Diffraction gratings ruled by Henry A. Rowland (1848-1901), working at Johns Hopkins University in Baltimore, on speculum metal blanks from John Brashear (1840-1920) were widely distributed. Three examples are shown below. The Kenyon grating, with a ruled surface one inch by two inches, has the following scratched in cursive letters on one side of the grating surface "Concave Grating Ruled by Scheneider [Rowland's mechanician] on Rowland Engine, Baltimore July 1885 Radius about 6 ft  14435/inch" On the other side is "Plate polished & Corrected by J. A. Brashear" In his autobiography, Brashear devotes an entire chapter to these gratings. He wrote "We were to furnish the plates, Rowland was to rule them and send them back to us, we were to act as distributing agents for them.... Several thousand of these plates were made at our shops [in Pittsburgh] and distributed  ...As I write this note more than thirty-five years later, we are still making those beautiful plates and distributing them to institutions of learning all over the world. Rowland has passed on and his ashes lie in a niche in the stone wall of the ruling-engine vault..."
         Bowdoin College                                       Kenyon College                         United States Military Academy

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