Consideration cf several of the present types of lanterns for the above purpose shows them as expensive and complicated. The article, however, here described, while offering little originality, exhibits simplicity and moderate cost, being well within the reach of the mass of examining oculists.
The apparatus consists of a Thorington's asbestos chimney, with iris diaphragm, and a double cell of half a trial frame attached in front of and below the circular opening in the chimney. The light within is either electric or gas; enclosed in a frosted bulb or chimney of an Argand burner.
The glasses for testing the colors are six in number, four being contained in the usual test-case: The red, the blue, the cobalt blue (for purple) and one for London smoke. This last can also be used in the several varieties furnished by the test-case. The remaining two necessary glasses, not found in the test-case,