Newton's Rings
   Isaac Newton first discussed the colored interference fringes that we now call Newton's Rings in a communication to the Royal Society in December 1675, and presented an expanded account in his book "Optics" (1705). The original observation was first made with a wedge-shaped air-gap between the surfaces of two prisms, but later used the now-standard technique of pressing the convex surface of a lens against a flat glass plate. The familiar colored rings are best observed in monochromatic light.
   The unusually-mounted Newton's Rings apparatus at the left is at Allegheny College in Meadville, Pennsylvania, and was made by Duboscq of Paris. 

    Allegheny has an example of an interference prism, another form of Newton's Rings, that was also made by Duboscq. 
 Duboscq also made these two examples of Newton's Rings apparatus. 

   At the left is a device from Allegheny College. It has a black flat plate to facilitate observation of the circular fringes by reflected light. 

   The example at the right is at Washington and Lee University in Lexington, Virginia. 
   The example at the right of Newton's Rings by reflection is by Duboscq, and is in use in the lecture rooms at Cornell University. The main lecture room has about two hundred seats, and so the demonstration can only be seen by use of a television camera and monitor.
   The cast iron parts of these two Newton's Rings demonstrations mark them as being made about 1900. 

   The apparatus at the left is from Colby College in Waterville, Maine; the apparatus at the right is at Kenyon College in Gambier, Ohio.

   Below are four examples of Newton's rings apparatus meant to be viewed horizontally. The example that I photographed on the floor carpet at the left below is at the United States Military Academy at West Point, New York, and was made by the firm of James W. Queen of Philadelphia; the one to its right I use at Kenyon College and is unmarked. The two in the lower picture
are at Union College in Schenectady, New York. Note that the one on the left is intended to be used by reflected light.

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