of each pipe is placed a burner, attached to a horizontal gas-pipe, which turns upon an axis.  The object of having this pipe rotate is to bring the burners into an inclined position—­shown by the dotted lines in Fig. 2—­for lighting them.  On turning them back to the vertical position, the heated products of combustion pass up the shorter tube and down the longer, where they enter a common receptacle, from which they pass into the chimney or out of doors.  Surrounding the pipes are plates of sheet iron, inclined at the angle shown in Fig. 2.  The object of the plates is to prevent the heated air of the room from passing up to the ceiling, and send it out into the room.  To prevent any of the pipes acting as chimneys, and bringing the products of combustion back into the room, as well as to avoid any back-pressure, a damper is attached to the outlet receptacle.  The heated gas becomes cooled so much (to about 100 deg.  Fahr.) that water is condensed and precipitated, and collects in the vessel below the outlet.  Each burner has a separate cock, by which it may be kept closed, half-open, or open.  To obviate danger of explosion, there is a strip of sheet iron in front of the burners, which prevents their being lighted when in a vertical position; so that, in case any unburned gas gets into the pipes, it cannot be ignited, for the burners can only be lighted when inclined to the front.  In starting the stove the burners are lighted, in the inclined position; the chain from the damper pulled up; the burners set vertical; and, as soon as they are all drawing well into the tubes, the damper is closed.  If less heat is desired, the cocks are turned half off.  It is not permissible to entirely extinguish some of the burners, unless the unused pipes are closed to prevent the products of combustion coming back into the room.  The consumption of gas per burner, full open, with a pressure of 8/10, is said to be only 4-3/8 cubic feet per hour.

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CONCRETE WATER PIPES.

Concrete water pipes of small diameter, according to a foreign contemporary, are used in parts of France, notably for water mains for the towns of Coulommiers and Aix-en-Provence.  The pipes were formed of concrete in the trench itself.  The mould into which the concrete was stamped was sheet iron about two yards in length.  The several pipes were not specially joined to each other, the joints being set with mortar.  The concrete consisted of three parts of slow setting cement and three parts of river sand, mixed with five parts of limestone debris.  The inner diameter of the pipes was nine inches; their thickness, three inches.  The average fall is given at one in five hundred; the lowest speed of the current at one foot nine inches per second.  To facilitate the cleaning of the pipes, man-holes are constructed every one hundred yards or so, the sides of which are also made of concrete.  The trenches are about