The refractive indices of all glasses at present available lie between 1.46 and 1 90, whereas transparent minerals are known having refractive indices lying considerably outside these limits; at least one of these, fluorite (calcium fluoride), is actually used by opticians in the construction of certain lenses, so that probably progress is to be looked for in a considerable widening of the limits of available optical materials; possibly such progress may lie in the direction of the artificial production of large mineral crystals. [Please select]
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For a long time opticians were unable to find a remedy. [Please select]
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Optical tests can be conducted by securing an ordinary letter chart such as is used by oculists and opticians. [Please select]
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If all women followed your example it would impoverish the opticians. [Please select]
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These cells are obtained from the opticians, and cemented with varnish or marine glue to an ordinary glass slide. [Please select]
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This is a fact recognized not only by opticians but by the world. [Please select]
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Such a low power is exceedingly well adapted for the examination of living insects, or of the exquisite preparations of entire insects, which can now be had of all opticians. [Please select]
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The opticians sell special pieces of apparatus for this purpose, but though they are very useful, they do not render it less desirable to have the mirror mounted as described. [Please select]
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