Dioptric Holophote

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“Perfect Form of Dioptric Holophote for an Oil Flame.—By combining the back prisms ga, hc just described with a semi-holophote abc subtending 180 degrees and a portion of the dioptric spherical mirror ijk, no light is lost on the burner, and all the rays are parallelized, so that this apparatus, being all of glass, is both geometrically and physically perfect.” —The Encyclopedia Britannica, 1910


The Encyclopedia Britannica, New Warner Edition (New York, NY: The Werner Company, 1893)


TIFF (full resolution)

1722×2400, 1.0 MiB

Large GIF

734×1024, 141.4 KiB

Medium GIF

459×640, 72.6 KiB

Small GIF

229×320, 26.7 KiB