SCIENTIFIC AMERICAN SUPPLEMENT, No. 6. 91 burner, and the hole in the latter measured nt. of an inch a size considerably smaller than we are in the habit of using, but chosen purposely to suit the limited space at our disposal in which to separate the photometer screen from the light. The gases were carefully adjusted till the light was at its best, and its value was then ascertained by a modification of Bunsen's photometer, in which the candle was fixed at a dis tance of one foot from the

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... n, and the two together moved away from the light until both sides of the disc were equally illuminated. This was repeated very many times, and ex amined by various observers, the result being that a mean of all the observations gave the value of the lime light, under the above conditions, as 115'5 standard candles. In the next experiment, coal-gas was substituted for the pure hydrogen, and, somewhat to onr snrprise, the result was not to any ap preciable extent different, the light being, both as shown by the photometer and in the judgment of those by whom we were assisted, in every respect equal to that given by pure hydrogen. Between each of the gas-bags and the burners we had in troduced one of the gas-meters, and carefnlly noted the rela tive quantities of gases conEumed, the result being that with pnre hydrogen it stood-oxygen 1, hydrogen 1'3; and with coal-gas-oxygen 1, hydrogen 1'1. We are aware that there is a very general belief that the proportions in which oxygen and hydrogen combine to form water (HoO) are those which ought to give the best results in raising the lime cylinder to the incandescent state; but those who have had much prac tice with lime-light exhibitions, where the bags have been of nearly the same size, know very well that the hydrogen bag, especially when coal-gas is used, does not get empty much sooner than the one containing oxygen. What may be the true explanation of the apparent anomaly we are not at present in a position to say; but the result of the somewhat careful measurements above recorded is quite in harmony with the opinion that we had formed from our experience with the practical working of lantern exhibitions. Of course it will be understood that in bringing the light up to only 115'5 candles, we were not seeking to produce the best effect that could be obtained, but only the best under the conditions named, with a view to comparing the pure hydro gen with coal-gas; and we may say that, on increasing the orifice of the jet to .08, and doubling the pressure, we more than quadrupled the illumination, and when it was passed through the ordinary lantern condenser it was roughly found eq nal to abont 405 candles To get at that estimate, however, the candle was fixed at only two inches from the photometer screen, and therefore there was some difficulty in deciding the precise distance from the light at which both sides became equally illuminated.