Page:Popular Science Monthly Volume 27.djvu/154

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ing amounts of moisture in the air materially affect health and comfort. Moist air is a better conductor of heat than dry air, hence we feel more chill in thaws than during crisp, cold weather. Fogs are injurious, net only on account of the vapors they contain, but because the air is saturated with moisture at a low temperature. Variations in temperature and pressure exert a considerable influence on the circulation of air contained in the soil (ground-air), and this frequently contains that which it is not well to breathe. Winds affect health directly by promoting evaporation from the skin and abstracting heat from the body, and indirectly by their influence on the temperature and pressure of the air. Scarlet fever prevails most when the mean temperature is between 45° and 57° Fahr. Diseases of the lungs are fatal in proportion to the lowness of the temperature and the presence of excess of moisture and fog. Relations appear to exist between a high summer temperature and mortality from diarrhœa. The relations between the weather and disease are not always uniform, for a discordance has been observed in the curves for whooping-cough, typhoid fever, and scarlet fever, between London and New York, and in diarrhœa between London and India. Better information is needed on this subject.


Spectro-photometric Study of Pigments.—Edward L. Nichols, Ph. D., in a paper read at the last meeting of the American Association on "A Spectro-photometric Study of Pigments," finds that the spectroscope shows that pigments can not be considered even in the roughest approximation as reflecting monochromatic light, but that they are more nearly related to white. Hence, "the attempt to express the hue of non-luminous bodies by comparison with isolated spectral tints is founded upon a false conception of the nature of the light which they reflect. To determine the hue of a pigment from the analysis of the light it reflects is a problem in physiological optics, the solution of which varies with the character of the observer's eye. The three primary color-curves of the eye must be determined, and the total intensity of each wave-length of the spectrum of the pigment must be divided in the proportions indicated by the color-curves into three components—red, green, and violet. Summing up each of these components for the entire spectrum, we obtain an expression for the hue in terms of the three color-sensations of which it is the resultant. In default of this method, which is difficult of execution, the curves themselves are an expression of the hue, the only requisite for the interpretation of which is practice in associating the sensation of color produced by pigments with the form of curve representing them."


The Manufacture and Applications of Iridium.—The manufacture of articles from iridium has recently assumed considerable importance through the discovery of practicable methods for making the metal. Iridium is obtained, in Russia and California, as a by-product in the working of the ores of platinum and gold, and is found only in the condition of grains, not larger than grains of rice, or of a fine powder, and often alloyed with platinum or osmium. It is one of the hardest substances known, being in that respect nearly the peer of the ruby, is not readily or permanently acted upon by oxygen, and is soluble in no single acid, and only slightly soluble in aqua regia. Its principal use hitherto has been for the pointing of gold pens, for which purpose the grains had to be taken as they were found, and soldered on without working over. The discovery of the process for working iridium is due to two gentlemen of Cincinnati, Mr. John Holland, a gold-pen manufacturer, who found that it could be melted with phosphorus; and Mr. W. L. Dudley, who devised a method for afterward eliminating the phosphorus. Mr. Holland, seeking larger pieces of iridium than could be found in Nature, discovered, after many experiments, that by heating it to a white heat and adding phosphorus, with a few minutes more of heating, he could obtain a perfect fusion, and could pour out the molten metal and get a casting of it. The product proved nearly as hard as the natural grains of iridium, and to have nearly all the properties of the metal itself, but, containing from 7·52 to 7·74 per cent of phosphorus, was liable to fusion, and could not therefore be used for purposes, as in elec-