A classification of electric motors shows them to be divided into groups according to their winding and the character of the current employed to operate them. The direct current is used for motors wound as follows: Constant current series-wound motors, constant potential shunt-wound motors, constant potential differentially wound motors. Each of these types is distinct as far as its winding is concerned, although the last is a combination of the first two - that is, shunt and series winding. Series-wound motors are employed on direct current circuits which supply a constant potential; they are used in high tension arc light constant current systems and in street railway 500-volt constant potential systems. The shunt-wound motor is used for stationary work, such as the running of machine tools, printing presses, etc.

Experiments in long-distance overland space telegraphy were made last year, says " Cassier's Magazine," and in the United States signals were transmitted a distance of about 300 miles between Chicago and St. Louis. There appears to be no crying demand, however, for a wireless telegraph service for public use between large cities, even if the entire practicability of the sytem for long distances overland had been satis-factorily'demonstrated; but the employment of this beautiful system, which has not yet ceased to be wonderful, between ships at sea and ships and the mainland, and between points divided by sea or lake, where the use of cables is not economically practicable, is steadily and rapidly increasing. Among the more recent important instances of this nature are the five Marconi stations on the river and Gulf of St. Lawrence, which cover a territory of nearly 1000 miles, and the De Forest Stations at Bocas det Terro, Panama, and Port Limon, Costa Rica, seventy miles apart.

A recent improvement in microscopy utilizes an entirely new principle of radiance. When ordinary sunlight is analyzed by a prism, the observer sees all the colors of the rainbow, there being at one end of the series a violet band and at the other a red one. The rays emanating from the former are shorter than the others. Out beyond the visible violet rays are others having a still shorter wave length, but ordinarily unseen. Glass obstructs them, but a prism of quartz transmits them. These " ultra violet " rays have a high photographic value. The astronomer is thus enabled to obtain records of lines in the solar spectrum which he cannot see. Some of the Jena experts have proposed to substitute quartz for glass in the train of lenses interposed between the arc light and the specimen, and also in the objective used for examination. Thus the visible light is reinforced by invisible light, the latter being particularly useful for obtaining a photograph of a specimen. The plan has the additional merit that the staining of a specimen before examining it would be unnecessary.

" Acid metal " or " lead bronze" is a durable alloy which can withstand the corrosive action of mine water. It is, therefore, suitable for machinery employed underground. Its ingredients are: 75 per cent, copper, 15 per cent, lead, 99 percent tin, and 0.10 per cent, phosphorus.

To test the purity of turpentine, drop a small quantity on a piece of white paper and expose to the air. No trace will be left if the turpentine is pine; but if it contains oil or other foreign matter, the paper will be greasy.

The underground railway system of London is operated only in part by electricity, steam locomotives still being employed on a number of the lines. When the electrification of all the subways is completed, as planned, one will be able to travel sixty miles underground without running twice over the same track.