Humboldt State University
Robert A. Paselk Scientific Instrument Museum
Humboldt State College, 1953
The polarizing microscope is a much an optical measuring instrument as it is an instrument for the detailed examination of specimens. In addition to standard microscope optics, there is a polarizer in the condenser and another mounted in a slider in the tube above the objective, both in rotatable, graduated, mounts. The specimen is illuminated with plane polarized light, and its rotation of this light can be analyzed. The polarizing microscope is particularly useful in the study of birefringent materials such as crystals and strained non-crystalline substances. It is widely used for chemical microscopy and optical mineralogy. The current specimen is equipped with a quick change, centering nosepiece and a graduated, rotating stage. The upper slider contains a Bertrand lens, to allow telescopic observation of the rear lens element of the objective. It is described by the manufacturer as suitable for routine work or for student use.
The microscope stands 340 mm high when closed. The heavy, cast iron, stand measures 103 mm from the optical axis to arm at stage level, and 132 mm from table to the stage. The fine adjustment is graduated to 0.0025 mm. The microscope is equiped with optical quality polaroid analyzer and polarizer. The stage is 125 mm in diameter with the periphery graduated in degrees, and readable by a vernier to three minute os arc. The instrument is complete with a gray leatherette covered carrying case with an AO Spencer No. 495 Graduated Attachable Mechanical Stage in a case, and a case for accessories, containing: four compensators (full-wave plate, 1st order red.; quartz wedge, I to III order; quarter wave plate; Becke aperture plate), three objectives (2x, 10x, & 43x) mounted on No. 463 objective centering rings (with 2 adjusting wrenches), two standard size cross-hair eyepieces (6x & 10x), and a pinhole eyepiece.
This instrument is described in detail and illustrated as the AO Spencer Polarizing Microscope No. P42AC on pg. F-7 of the AO Spencer Instrument Division Catalog (c. 1953). The HSU inventory listed this instrument as being acquired in 1953.
According to Dr. John B. Russell (HSU Chem. Dept. 1956-92) this microscope was probably purchased by Harry MacGinitie who headed the Natural Sciences division (est. 1947, split to Biol. and Phys Sci in 1960). Professor MacGinitie had a research interest in paleopollen, and studied local deposits. This microscope may have been purchased with this research in mind.
© R. Paselk