rod strikes smartly and sharply upon the spring, N T. Contact between T and H is broken, and the current passes through the electromagnet of the break in the lamp. The break is released for an instant, the carbons approach each other. But the same rupture of contact introduces in the shunt a new resistance of considerable magnitude (viz., 1,200 ohms), that of the electromagnets of the break. Then the strength of the shunt current diminishes considerably, and the solenoid, S, recovers briskly its drawing power upon the rod, and contact is restored. The carbons approach during these periods only about 0.01 to 0.02 millimeter. If this is not sufficient to restore equilibrium it is repeated continually, until equilibrium is obtained. The result is that the carbon is continually falling by a motion invisible to the eye, but sufficient to provide for the consumption of the carbons. [Illustration: FIG. 6] The contact between N T and H is never completely broken, the sparks are very feeble, and the contacts do not oxidize. The resistances inserted are so considerable that heating cannot occur, while the portion of the current abstracted for the control is so small that it may be neglected. The balance acts precisely like the key of a Morse machine, and the break precisely like the sounder-receiver so well known in telegraphy. It emits the same kind of sounds, and acts automatically like a skilled and faithful telegraphist. This regulation, by very small and short successive steps, offers several advantages: (1) it is imperceptible to the eye; (2) it does not affect the main current; (3) any sudden instantaneous variation of the main current does not allow a too near approach of the carbon points. Let, now, an accident occur; for instance, a carbon is broken. At once the automatic cut-off acts, the current passes through the resistance, R, instead of passing through the lamp. The current through the fine coil is suddenly increased, the rod is drawn in, contact is made at G and K, and the current is sent through the coil, R. As soon as contact is again made by the carbons, the current in the coil, S, is increased, that of the thick wire in V diminished, and the antagonistic spring, U, breaks the contact at G and K. The rupture of the light is almost invisible, because the relighting is so brisk and sharp. I have seen this lamp in action, and its constant steadiness leaves nothing to be desired. * * * * * APPARATUS FOR OBTAINING PURE WATER FOR PHOTOGRAPHIC USE. Our readers are well aware that water as found naturally is never absolutely free from dissolved impurities; and in ordinary cases it contains solid impurities derived both from the inorganic and organic kingdoms, together with gaseous substances; these latter being generally derived from the atmosphere.