142 



THE POPULAR SCIENCE MONTHLY. 



ing amounts of moisture in the air materi- 

 ally 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 in- 

 jurious, net only on account of the vapors 

 they contain, but because the air is satu- 

 rated with moisture at a low temperature. 

 Variations in temperature and pressure ex- 

 ert a considerable influence on the circula- 

 tion 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 di- 

 arrhoea. 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 scar- 

 let fever, between London and New York, 

 and in diarrhoea between London and India. 

 Better information is needed on this sub- 

 ject. 



Speetro-pbotomotric 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 spectro- 

 scope shows that pigments can not be con- 

 sidered even in the roughest approximation 

 as reflecting monochromatic licrht, 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 op- 

 tics, 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 spec- 

 trum, 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 interpre- 

 tation 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 



Iridiin 1. The manufacture of articles from 

 iridium has recently assumed considerable 

 importance through the discovery of practi- 

 cable methods for making the metal. Irid- 

 ium 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 oft- 

 en 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 rcgia. Its 

 principal use hitherto has been for the point- 

 ing 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 eliminat- 

 ing 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 nat- 

 ural grains of iridium, and to have nearly all 

 the properties of the metal itself, but, con- 

 taining from 7"52 to 7*74 per cent of phos- 

 phorus, was liable to fusion, and could not 

 therefore be used for purposes, as in elec- 



