β Scribed by C.
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Strengtli of Slate.--Messrs. Blavier & Brossard, mining engineers, have studied the comparative resistance to rupture of the Angers slates, marble, and Tonnerre stone. The experiments were made with slabs of about 1 metre long, "15 to "50 metres wide, and '008 to "050 metres thick. The rupturing load P was weighed, and the coefficient of rupturing resistance R was calculated by the formula, P (5--a) p R 1 e 2 " 4 6 in which 1 is the distance between the supports, b the breadth of slab, e its thickness, and a the breadth of the ledges. The following mean values were found for//: for slate cut lengthwise, 5,621,000 ; slate cut crosswise, 2,788,000; marble, 1,140,000; Tonnerre stone, 680,-400. Slate has the added advantage of being easily split into slabs, while the other stones require the use of a saw.--Ann, des _P. et Chauss. C. Parisian Libraries.--The National Library contains more than a half million volumes. Other city libraries aggregate more than 1,100,000 volumes.--Les Mondes. C. Electro-Silicic Light.--M. G. Plantg has obtained very brilliant effects by placing one of She poles of a powerful secondary battery in contact with the side of a glass vase or a porcelain basin, holding a saline solution. The luminous appearances observed in glass, under induction currents, by du Moncel, Gassiot, Grove and others, also accompany the new process. The same results may be obtained by substituting rock-crystal for the glass or porcelain, but a higher power is required.roLes Mondes. C. Safety of Railroad Traveling.--The Annales des _Ponts et Ohaussdes, for August and September, 1877, contain two valuable articles on the "Block System" of running trains. From the second article We extract the following statistics. The average loss of life in France, in traveling by diligence, was 1 in 355,000 ; on railroads, from 1835 to 1855, 1 in 2,000,000; from 1855 to 1875, 1 in 6,000,000; from 1872 to 1875, 1 in 45,000,000. A person traveling constantly by railroad, for 10 hours a day, at the rate of 50 kilometres per hour, estimating a mean journey at 30 kilometres, would have had the following chances of being killed by a railroad accident: 1835 to 1855, 1 chance in 321 years; 1855 to 1875, 1 chance in 1014 years; 1872 to 1875, 1 chance in 7459 years. ~ C.
π SIMILAR VOLUMES
Electrooptical modulators using the linear electrooptic effect on ADP, KDP, DKDP, and LiNbO, crystals have been developed. The modulator of the Billings cell type needs a modulation voltage of some kV. Its great advantage is a large aperture and a simple construction. For the modulation of a laser b