German papers state that the " Great Grocery Exhibition," an association of large dealers in groceries in England, has now for the fifth time offered a prize for a safety lamp using mineral oil, A lamp is wanted which shall not cost more than 50 cents and which, regardless of any ignorance or carelessness, must not be more dangerous than a common candle. The problem seems to be hard to solve, as a prize has already been offered four times heretofore. Many lamps haye, of course, been received for competition, but so far none has satisfied the judges. That such a lamp would be of great value is apparent from the fact that during last year no less than 256 fires, about 5 each week, in the London district were due to petroleum lamps.

Silver can be rolled into sheets 1-1000 of an inch in thickness, and silver foil is made so thin that it will transmit light.

The Bonis electric sweeper, cleaner, and ventilator is a portable arrangement, consisting of an aspirator with 1-16 h. p. motor and suction attachment, and separator or dust filter. The brushes, which are attached to a hollow pole like a broom handle, or moved by hand, are bell-shaped, and have bristles arranged around the outer rim in such a manner that the air can pass freely through them. The suction produced in the center of the brush by the motor draws into the receptacle the dust, dirt, fluff, etc., removed in the sweeping. India-rubber brushes are used for fragile objects, furniture. etc. The air being loaded with dust is caused to pass through a separator provided with a number of cells for retaining the dust, after which the filtered air is passed through a canvas bag out into the open. The receiving chamber can be made metal and provided with a disinfecting fluid, thus deodorizing all sub-stances as they enter. The mechanical part of the apparatus, provided with motor and exhauster, can be used as a ventilator.

The operation of producing liquid air is briefly as follows: Air is compressed to 1200 lbs. to 2000 lbs to the square inch; passed into receptacles where it is purified by separating the moisture, oil, etc., and passed thence into expansion chambers and through coils of pipe of considerable length. During the process it becomes intensely cold, reaching finally 312° be-low zero, at which point it becomes liquid. It is drawn off into insulated vessels, where it is kept for days, gradually lessening in quantity until it is entirely evaported.

The dust of meteorites that undergo complete combustion on contact with the earth's atmosphere has been traced on the earth's surface as for instance, in the inland ice of Greenland in the shape of particles of magnetic iron with cobalt. This same character of dust has also been found at a number of places in northern regions, and it is known as cosmic dust.

Kinetic energy is the power stored in a moving object which keeps it in motion. By way of illustration, conceive a railway train rushing along a straight, level stretch of track, the train being driven to its power limit. If the source of power, say the steam pressure, is now suddenly removed by closing the throttle, the train will continue to run or "coast," for a long distance, due to its kinetic energy, gradually reducing in speed until the energy is exhausted and the train stops.