The outstanding feature of this apparatus is that the clockwork control cutting off and turning on the gas does not require to be wound by hand, but is actuated by the mechanism which revolves the lenses, through a simple set of gearing. The gas as it issues from the reservoir passes into one of two cylinders. Each of these is provided with an inlet and an exhaust valve, while the upper end is closed with a lid of leather, covering the top like the vellum of a drum. To each leather cover is attached a circular piece of metal, smaller than the leather diaphragm, and from this in turn extends a vertical rod, the upper end of which is connected to one end of a centrally pivoted rocking arm. When the gas enters one cylinder, naturally in expanding it forces the leather lid upwards, and with it the vertical rod. This elevates the corresponding end of the rocking arm, and simultaneously drives down the rod attached to the opposite end of the beam, which in turn drives down the leather lid of the second cylinder, and forces out any gas that may be therein. The apparatus consequently is something like a double pump, owing to the rocking arm having a seesaw motion. This reciprocating action serves to wind up the clock, and also to revolve the lenses through spurs and pinions. The mechanism, however, is controlled completely by the clock whereby the light is started, inasmuch as without this the apparatus cannot be set in motion. There are two dials, one of which is divided into twenty-four divisions, corresponding to the hours of the day, and the other into twelve divisions, representing the twelve months of the year. The clocks work together, and the time of lighting up is advanced or retarded, according to the time of the year, through the clock train wheels. The apparatus is very compact, highly ingenious, and has proved efficient in service. Although this is the first application of the idea for rotating the lenses by the gas which feeds the burners, so far as England is concerned, it has been employed under similar circumstances in Germany with conspicuous success, in combination with the Pintsch oil-gas apparatuses, but it lacks the simplicity and reliability of the sun-valve. [Illustration: AN UNATTENDED BEACON LIGHTING THE STRAITS OF MAGELLAN. This warning, fitted with Dalén flasher and sun-valve, is visited once in six months.] [Illustration: AN AUTOMATIC LIGHT-BOAT. This novel warning was constructed for installation at the mouth of a Swedish river owing to the extreme velocity of the current. Such a boat may be left unvisited for a year if desired.]