THE POPULAR SCIENCE MONTHLY.
emits no smoke. Probably its greatest advantage is to be found in the influence it exerts on health. At Glasgow, where the light has been applied, all causes of trouble arising from the vitiation which was occasioned by other lights have ceased. Health has been engendered, and more work has been got out of the men; and experience has shown that the electric light will pay for itself in the superior return it makes in this point alone.
Mr. Preece has published in a separate paper some facts bearing upon the economy of the electric light. The Loan Court of the South Kensington Museum, a room not favorably arranged for the diffusion of light, has been lighted for nine months with sixteen Brush lamps, at a cost for working of 3s. 10d. per hour of light. Had gas been used, a consumption of sixteen hundred cubic feet per hour would have been required, at a cost of 16s. Considering that the museum is lighted up) for seven hundred hours every year, the total saving effected by the use of electricity is at the rate of £426 or $2,130 a year. It is fair, however, to add something for the use of the capital, wear and tear, etc., to the annual expense. Reckoning this at five per cent, all around, the annual saving is still £316 10s., or $1,580. The reading-room of the British Museum is lighted by the Siemens electric light, at a cost of 5s. 6d. per hour, one third of what would be required for gas, were it used. A shed at the sugar-refinery of Messrs. Henry Tate & Sons, Silvertown, is lighted by a Crompton lamp in the ceiling, assisted by a canvas reflector. The whole of the shed is well lighted—four or five times more strongly than with gas—and the light penetrates an adjoining shed. The cost for fourteen hours of illumination is 1s. 9d., or 1½d. an hour; the cost of illumination by gas was 3s. 6d., or 3d. an hour. At the ship-building dock, Barrow-in-Furness, a work-shed is lighted by Brush lights at £4 14s. a week, where oil blast-lamps were formerly used at £8 9s. a week; and the erecting-shop, formerly dimly lighted by gas at £22 a week, is now efficiently lighted by electricity at half the cost.
By Dr. ANDREW WILSON.
IN groups of the animal series, both nearly allied to the crustacean class and far removed from it in structure, equally interesting and often curious examples of degradation may be found. The class of insects and the nearly related group, including the mites, spiders, and scorpions as its representatives, number in their ranks instances of degraded and degenerate forms. Among the insects which are parasitic in habits a notable absence of wings is discernible, and this