As a standard lamp by which to test others, I believe few will be found superior to the best Carcel lamp, which has a clockwork movement, and whose flame continues to increase in power for about four hours after it is lighted; after which it maintains its state permanently, until the supply of oil fails. This fact was verified by M. Peclet with the greatest care. “I took,” says he, “two similar lamps. They were lighted at the same time, and their relative intensities were measured. One was then extinguished, without touching the wick, and its clockwork movement was stopped. One hour afterwards, I set the clockwork in motion and relighted the lamp, but without touching the wick. It was found in the same state as at the first comparison, and I measured its intensity in reference to the first. Those experiments I repeated every hour, and these are the results which I obtained. The lamp which I call No. 1, is that which remained continually burning; No. 2, is that which was only lighted during the continuance of the (successive) observations.” +------------++-------------------------+ | || Intensities. | | Times of ++------------+------------+ |Observation.||Lamp, No. 1.|Lamp, No. 2.| +-----+------++------------+------------+ | H. | M. || | | | 5 | 30 || 100 | 100 | | 6 | 30 || 103 | 100 | | 7 | 30 || 106 | 100 | | 8 | 30 || 110 | 100 | | 9 | 30 || 117 | 100 | | 10 | 30 || 117 | 100 | | 11 | 30 || 117 | 100 | | 12 | 30 || 117 | 100 | +-----+------++------------+------------+ This curious scale of increase in power, seems to be solely due to a peculiarity of the manner in which the lamp, that derives its supply of oil by clockwork, becomes heated; and the effect may be described as follows: The heating of the wicks, the chimney, and the oil in this burner, as in that of all other lamps, tends to increase the light; but, in an ordinary lamp, acting by a constant pressure, this _maximum_ of heat is soon attained; whereas in the clockwork-lamp, into the burner of which the oil is thrown up by a pump, the whole of the oil in the cistern must reach its maximum temperature before the _best_ effect of that lamp is produced. After this state has been reached, there is no disturbing influence at work, and the lamp burns steadily as long as the oil lasts.