I have found all the products of distillation from the copper still capable of burning well in the camphene lamp, except the last third or fourth part (i.e., that portion which came off at 700° F. and rising, and which was thick with the crystals of paraffine). Freed from acidity by boiling on water, the oils of this distillation burned for twelve hours without injuriously coating the wick, and without smoke. The wick may be elevated considerably above the level required for camphene, without any danger of smoking, and the oil shows no signs of crusting the wick tubes with a coating of rosin, such as happens in the case of camphene, and occasions so much inconvenience. The light from the rectified naphtha is pure and white, without odour. The rate of consumption is less than half that of camphene, or rosin oil. The Imperial pint, of 20 fluid ounces, was the one employed—a gallon contains 160 such ounces. A camphene lamp, with a wick one inch thick, consumed of rectified naphtha in one hour, 1¾ ounces of fluid. A Carcel’s mechanical lamp of ⅞–inch wick, consumed of best sperm oil, per hour, 2 ounces. A “Diamond Light” lamp, with “sylvic oil,” and a wick 1½–inch diameter, consumed, per hour, 4 ounces. I have submitted the lamp burning petroleum to the inspection of the most experienced lampists who were accessible to me, and their testimony was, that the lamp burning this fluid gave as much light as any which they had seen, that the oil spent more economically, and the uniformity of the light was greater than in camphene, burning for twelve hours without a sensible diminution, and without smoke. I was, however, anxious to test the amount of light given, more accurately than could be done by a comparison of opinions. With your approbation I proceeded therefore to have constructed a _photometer_, or apparatus for the measurement of light, upon an improved plan. Messrs. Grunow, scientific artists of this city, undertook to construct this apparatus, and have done so to my entire satisfaction. This apparatus I shall describe elsewhere—its results only are interesting here. By its means I have brought the petroleum light into rigid comparison with the most important means of artificial illumination. Let us briefly recapitulate the results of these PHOTOMETRIC EXPERIMENTS The _unit_ adopted for comparison of intensities of illumination is Judd’s Patent Sixes Sperm Candle. The sperm oil used was from Edward Mott Robinson, of New Bedford—the best winter sperm remaining fluid at 32° F. The colza oil and Carcel’s lamps were furnished by Dardonville, lampist, Broadway, New York. The gas used was that of the New Haven Gas Light Co., made from best Newcastle coal, and of fair average quality.