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This paper presents the most important considerations in the design and construction of polariscopes for routine factory use as found in the author's experience. A short summary of the various methods of obtaining plane-polarized light is given in which preference is given to the reflection method for this type of instrument. The use of binocular analyzers, together with the importance of the matching of the field colors due to the tint-plates, is pointed out.

A phosphor containing alumina, lithia, and iron oxide is described. It is efficiently excited by 2537 A radiation, emitting a band spectrum with its energy peak at 6800 A and half its peak energy intensity at 6520 and 7320 A.Silica enhances the fluorescence, with a broad composition optimum at about the ratio 1 mol alumina, 0.3 mol lithia, 0.15 mol silica, 0.002 mol ferric oxide. Firing temperatures and times are not critical, 1250°C. for 2 hours is suitable. The firing is done in open containers.Much of the lithia may be leached from the phosphor, as by acids, without reducing the fluorescence. The leached phosphor may be reheated to at least 900°C. without impairing the fluorescence, but refiring in the 1250°C. region reduces the fluorescence to that which would be obtained by an initial firing of a batch having the composition of the leached phosphor.