some wedge interposed between the frames of the con- observations made by Mr. H. A. Smith, illustrate this densers. By reason of this adjustment a proper regis- very clearly. The measurements were made to deter- tration of the two pictures projected by the two optical mine the effect of current… … dirt, thus avoiding the use of a cyanide or an acid dip. cee Ce _ AWA A A metal which has a brightly polished surface may be A NEW FORM OF STEREOPTICON. cleaned without destroying the polish. 0+ - —-____ front, closes both the rectangular portion and an open- lenses, having a prism interposed…
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