These are arranged on the arms carrying the pawls, and so adjusted that no contact is made until after the toothed wheel has moved a degree, when a circuit is closed and a magnet attracts an armature attached to a pendulum.  This pendulum, after starting, breaks the circuit of the magnets which hold the pawls down, as well as of the short-circuiting device.  As the pendulum takes an appreciable time to vibrate, this allows all the magnets to drop back, and breaks all circuits, leaving the primary contacts in the same relation as at first.  The many details of the instruments are carefully worked out.  All the contacts are of a rubbing nature, thus avoiding danger from dirt, and they are made with springs, so as not to be affected by jar.

The receiving instruments can be made recorders also by simple devices.  Thus, having only a most delicate pressure in the primary instrument, a distinct ink record may be made in the receiver, even though the paper be rough and soft.  The method is applicable to steam gauges, water indicators, clocks, barometers, etc., in fact, to any measuring instrument where a moving hand can be employed.

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A NEW MONSTER REVOLVING BLACK ASH FURNACE AND THE WORK DONE WITH IT.

By WATSON SMITH, Lecturer in Chemical Technology in the Victoria University, etc.

The Widnes Alkali Company, limited, to which I am indebted for permission to describe this latest addition to a family of revolving black ash furnaces, of late not only increasing in number, but also individual size, has kindly allowed my friend, Mr. H. Baker, to photograph the great revolver in question, and I have pleasure now in throwing on the screen a picture of it, and also one of a revolver of ordinary size, so as to render a comparison possible.  The revolver of ordinary size measures at most 181/2 ft. long, with a diameter of 121/2 ft.  The boiling down pans connected with such a furnace measure 60 ft. in length.  Each charge contains four tons of salt cake, and some of these revolvers get through 18 tons of salt cake per day and consume 13 cwt. of coal per ton of cake decomposed.

With regard to the larger revolver, it may be just said that the Widnes Alkali Company has not at once sprung to the adoption of a furnace of the immense size to be presently given, but in 1884 it erected a revolver only about 3 ft. to 4 ft. short of the length of that one, and having two discharging holes.  The giant revolving furnace to be described measures in length 30 ft. and has a diameter of 12 ft. 6 in.  Inside length is 28 ft. 6 in., with a diameter of 11 ft. 4 in.  It is lined with 16,000 fire bricks and 120 fire-clay blocks or breakers, weighing each 11/4 cwt.  The bricks weigh per 1,000 about four tons.  The weight of salt cake per charge (i.e., contained in each charge of salt cake, limestone, mud, and slack) is 8 tons 12 cwt.  For 100 tons