From this table it will be seen that the rock-oil lamp was somewhat superior in illuminating power to Carcel’s lamp of the same size, burning the most costly of all oils. It was also equal to the “Diamond Light” from a lamp of one-half greater power, and consequently is superior to it in the same ratio in lamps of equal power. The camphene lamp appears to be about one-fifth superior to it, but, on the other hand, the rock-oil surpasses the camphene by more than one-half in economy of consumption (i.e., it does not consume one-half so much fluid by measure), and it burns more constantly. Compared with the sylvic oil and the sperm, the rock-oil gave on the ground glass diaphragm the whitest disc of illumination, while in turn the camphene was whiter than the rock-oil light. By the use of screens of different coloured glass, all inequalities of _colour_ were compensated in the use of the photometer, so that the intensity of light could be more accurately compared. Compared with gas, the rock-oil gave more light than any burner used except the costly Argand consuming ten feet of gas per hour. To compare the _cost_ of these several fluids with each other, we know the price of the several articles, and this varies very much in different places. Thus, gas in New Haven costs $4 per 1,000 feet, and in New York $3.50 per 1,000, in Philadelphia $2.00 per 1,000, and in Boston about the same amount. Such sperm oil as was used costs $2.50 per gallon, the colza about $2, the sylvic oil 50 cents, and the camphene 68 cents; no price has been fixed upon for the rectified rock-oil. I cannot refrain from expressing my satisfaction at the results of these photometric experiments, since they have given the oil of your company a much higher value as an illuminator than I had dared to hope. USE OF THE ROCK-OIL AS A LUBRICATOR FOR MACHINERY A portion of the rectified oil was sent to Boston to be tested upon a trial apparatus there, but I regret to say that the results have not been communicated to me yet. As this oil does not gum or become acid or rancid by exposure, it possesses in that, as well as in its wonderful resistance to extreme cold, important qualities for a lubricator. CONCLUSION In conclusion, gentlemen, it appears to me that there is much ground for encouragement in the belief that your company have in their possession a raw material from which, by simple and not expensive process, they may manufacture very valuable products. It is worthy of note that my experiments prove that nearly the _whole_ of the raw product may be manufactured without waste, and this solely by a well-directed process which is in practice one of the most simple of all chemical processes.