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Liquid Spectroscopes

The use carbon, for the manufacture of lenses, is makof transparent liquids, such as bisulphide of ing rapid progress on the ground of economy; ish, being difficult to obtain, and expensive. large pieces of glass, free from flaw and blem- Poggendorff's "Annalen" calls attention to possible disturbances of the accuracy of liquid prisms, the lines in the spectrum varying with changes of heat and cold, of the lines of solid the temperature. The divergence, owing to , owing to heated in the sun and then removed to the prisms, is quite insignificant. A glass prism, refractive power as it cooled, while a bisulshade, was observed to possess an increased phide prism exhibited a reversed result. These facts point out the importance of the use of the thermometer in conjunction with the spectroscope, and also show that there is room for great improvement in the manufacture of glass for optical purposes. for Windows. A hot solution of sulphate 2365. Prismatic Diamond Crystals of magnesia, and a clear solution of gum-arabic, mixed together. Lay it on hot. For a margin or for figures, wipe off the part you wish to remain clear with a wet towel.