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Click Here For Best Selection Of High Quality Polarizing Microscope

Click Here For Best Selection Of High Quality Polarizing Microscope

When minerals are to be examined between crossed nicols, both analyzer and polarizer but be placed in the axis of the microscope. And moreover, the two nicols must be rotated to such positions that, with an empty stage, no light reaches the eye. In order to simplify this adjustment each nicol is provided with a catch, which indicates the correct position. It must be borne in mind that if the two nicols are used, they must be in the crossed position, and neither maybe rotated. Rotation of the stage, however, is not only permissible, but also essential. We have already discussed that the light transmitted by the polarizer vibrates only parallel to the E.W., the principal section line. The analyzer is similar to the analyzer in all respect except that of position. Its principal section is in the N.S. direction. The result of this crossing of the two nicols is that the emerging extraordinary ray of the polarizer becomes the ordinary ray of the analyzer, and is totally reflected from the film of the balsam. With an empty stage, the polarized light from the lower nicol is allowed a free passage to the upper nicol, and, consequently, the whole of the light transmitted by the lower is stopped by the upper. The field is quite dark.

 

            A plate of glass, or any other singly refracting substance placed upon the stage does not produce any alteration of this condition. The reason being that it has no power to change the vibration direction of the entering light. Canada balsam is another singly refracting substance, hence we are quite certain that if any alteration is produced in the dark field when a microscope slide is placed on the stage, such alteration is due entirely to the minerals in the slide.



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Wednesday, February 13th, 2008 at 3:56 am
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Characters of Minerals Between Crossed Nicols
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