The instruments in general use at present for observing and photographing petrographic sections in plane or crossed polarized light limit the area under observation to a few square centimeters or less. Where it is desirable to magnify considerably the area, this restriction is not in the least a handicap. However, when the material is of such a nature that larger areas are required to show the relationship of the unit parts, “polaroid”,1 the new light polarizer, makes it possible to observe or photograph the entire area of any large thin section. The area is not limited to square inches or even square feet if larger dimensions are desired.

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