Norrenberg Doubler
   The Nörrenberg doubler (to give it its usual spelling) dates from 1858 and is a generalized apparatus for viewing transparent objects between crossed polarizing filters. The basic plan is shown at the right: a light beam A reflects at Brewster's angle from a glass plate D, passes through the object E before and after reflecting from mirror C, and then passes through the glass plate and reaches the eye at the top. The light is linearly polarized by reflection and then by transmission.

REFERENCE: Thomas B. Greenslade, Jr., "An Inexpensive Modern Norrenberg Doubler", Phys. Teach., 19, 626-627 (1981)

These Norrenberg doublers have more features. At the far left is one from Kenyon College that has a Nicol prism eyepiece at the top through which the effects are observed. It was made by Duboscq of Paris.

The Bowdoin apparatus at the near left is by Ferdinand Ernicke of Berlin.

   The upper ring is graduated in degrees so that the effects of optical rotation can be measured.

The incoming light can be polarized by reflection from the diagonal glass plate, and the sample placed above the mirror. 

   The Norrenberg apparatus at the far right is at Miami University in Oxford, Ohio. It was too fragmentary to work with, except that it was by Max Kohl of Chemnitz. 

   Subsequently the apparatus at the near right came into the Greenslade collection, and now I was able to see more details. 

   Both of these have polished granite bases typical of Kohl apparatus of the early part of the 20th century, and can be found in the 1925 Kohl catalogue. The more complete apparatus, complete with a (missing) column of plates polarizer on top of the stand, cost 252 marks. 

  At the left is another Max Kohl Norrenberg Polarimeter, dating from the later 1920s when it was bought by the physics department of Hobart and William Smith Colleges in Geneva, New York.

   I have actually never seen a complete Norrenberg apparatus in the United States.

   All three Norrenberg doublers below are at St. Patrick's College, Maynooth, Ireland. They are all by Duboscq of Paris.
   The Norrenberg Doubler at the left is listed in the records of the Denison University Physics Department as being made in 1880 by W. L Clouse. Some of the metal parts have a professionally-finished look. 

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