VIII. ORDNANCE.--Firing Trial of the 110½ Ton B.L. Elswick Gun. Full dimensions of this piece and it projectiles.--Results of proof firing.--9 illustrations. IX. PHOTOGRAPHY.--Experiments in Toning Gelatino-Chloride Paper.--Trials of ten different gold toning baths, formulas, and results. Printing Lantern Pictures by Artificial Light on Bromide Plates from Various Sizes.--By A. PUMPHREY.--The processor producing smaller or larger transparencies from negatives.--1 illustration. X. PHYSICS.--A New Mercury Pump.--Simple air pump for high vacua.--1 illustration. The Laws of the Absorption of Light in Crystals.--By H. BECQUEREL. Varying Cylindrical Lens.--By TEMPEST ANDERSON, M.D., B. Sc.--Combination of two conoidal lenses.--Range of power obtained. XI. PHYSIOLOGY.--Elimination of Poisons.--Treatment of poison cases by establishment of a strong diuresis. The Filtration and the Secretion Theories.--Experiments on the action of and secretions of the kidneys. XII. TECHNOLOGY.--Furnace for Decomposing Chloride of Magnesium.--Furnace with rotating chamber for use by alkali manufacturers.--1 illustration. Notes on Garment Dyeing.--The production of blacks on silk and wool.--Formulas for mordants. Studies in Pyrotechny.--II. Methods of Illumination.--Continuation of this valuable treatise.--9 illustrations. The "Sensim" Preparing Box.--New machine for treatment of fiber.--An improvement on the ordinary gill box.--3 illustrations. * * * * * THE RETIRO VIADUCT. We give engravings of the viaduct over the river Retiro, Brazil, our illustrations being reproduced by permission from the Proceedings of the Institution of Civil Engineers. In a "selected paper" contributed to the volume of these proceedings just published, Mr. Jorge Rademaker Grunewald, Memb. Inst. C.E., describes the work as follows: [Illustration: VIADUCT OVER THE RETIRO, BRAZIL.] This viaduct was constructed in the year 1875, according to designs furnished by the author, for the purpose of passing the Dom Pedro Segundo State Railway over the valley which forms the bed of the river Retiro, a small confluent on the left bank of the river Parahybuna. It is 265 kilometers (165 miles) from Rio de Janeiro, and about 10 kilometers (6.4 miles) from the city of Juiz de Fora, in the province of Minas Geraes, Brazil. It has a curve of 382 meters (1,253 ft.) radius, and a gradient of 1 in 83.3. Its total length is 109 meters (357 ft. 7 in.); width between handrails, 4 meters (13 ft.); and greatest height above the bed of the river, 20 meters (65 ft. 7 in.).