Nature . nd projects slightly, so that theoperator has a clear view up and down the the switch-board the energy is distributed to thevarious substations situated at various points along thesystem, and it is there converted to low-voltage directcurrent at 550 volts, and thence distributed to the liverail. Throughout the whole station it is remarkable to 38 grains of Anthonys pure snowy cotton in 2.\ ounces ofpure amyl acetate, precipitating the resultant collodion ina large tray of pure water—constantly agitating themixture—thoroughly drying the precipitate, and then re-dissolv
Nature . nd projects slightly, so that theoperator has a clear view up and down the the switch-board the energy is distributed to thevarious substations situated at various points along thesystem, and it is there converted to low-voltage directcurrent at 550 volts, and thence distributed to the liverail. Throughout the whole station it is remarkable to 38 grains of Anthonys pure snowy cotton in 2.\ ounces ofpure amyl acetate, precipitating the resultant collodion ina large tray of pure water—constantly agitating themixture—thoroughly drying the precipitate, and then re-dissolving it in the same quantity of pure amyl collodion thus obtained is carefully filtered, and isthen ready for use. The grating to be copied is levelled in a roomy dryingcabinet, which, in order to preclude dust particles, shouldbe as free from draughts as possible, the surface dustedwith a soft camel-hair brush, and the collodion flowedever it evenly. The author uses about twenty-five drops. K W. I ieneralcr find the extent to which labour-saving devices areemployed. Thanks are due to Mr. Chapman, general manager andchief engineer, for permission to view the station, and tothe Institution of Electrical Engineers for the accompanyingillustration of the armature of one of the generators. REPLICAS OF DIFFRACTION GRATINGS. I7ROM an article in No. 2, vol. xxii., of the Astro-physical Journal, we learn that Mr. R. J. Wallace,of the Verkes Observatory, has attained great perfectionin the production of replicas from plane diffraction some amount of previous research, he decided onfollowing Thorps method in its essentials with severalmodifications which his experience suggested. Mr. Thorpfirst flooded his original grating with high-grade oil beforepouring on the celluloid solution on which the replica wasmade. Mr. Wallace found it better to omit the oil. Inthe original method a solution of gun-cotton in amylacetate with camphor added was employed as the mat
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