Page:Popular Science Monthly Volume 11.djvu/133

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whom 630 were in Cincinnati, 549 in New York, and 300 in Brooklyn. Of the 630 Cincinnati pupils, 209 were from the district-schools, and of these 8312 per cent, had natural, or emmetropic eyes, while 10 per cent, were near-sighted. In the intermediate schools, 210 scholars were examined, and of these 80 per cent, were natural, and 14 per cent, near-sighted. In the normal high-schools, the eyes of 210 students were examined, and of these 78 per cent, were emmetropic, and 16 per cent, nearsighted. All this goes to show that nearsightedness is a progressive disease in the schools. The results for the other two cities teach the same lesson.

The 549 students mentioned above as examined in New York belonged to the New York College. Here, in the introductory classes, 5712 per cent, were found emmetropic, and 29 per cent, near-sighted. In the freshman class 4212 per cent, had natural eyes, and 40 per cent, were near-sighted. In the sophomore class no very material difference from what was observed in the preceding classes; but in the junior class 37 per cent, had natural eyes, and 56 per cent, were near-sighted. In the senior class 50 per cent, had normal eyes, and 37 per cent, were near-sighted. The Brooklyn students examined belonged to the Polytechnic Institute of that city. Here, in the academic department, 56 per cent, were emmetropic, and 10 per cent, near-sighted. In the collegiate department (a higher grade), 53 per cent, were emmetropic, and 2812 per cent, were near-sighted.

Astronomical Observations on the Rocky Mountains.—It is stated by Prof Henry Draper, in the February number of the American Journal of Science, that, during two years when he photographed the moon every moonlight night at Hastings-on-the Hudson, there were only three occasions when the air was still enough to give good results. Out of 1,500 lunar negatives, only one or two were really fine pictures.

Last summer, during a trip to the Rocky Mountains, he took with him a small achromatic, hoping to find more steadiness of the atmosphere at great elevations, but was disappointed. At Salt Lake City, 4,650 feet above the sea, Capella twinkled as badly, both to the naked eye and in the telescope, as he ever saw it at the sea-level.

At Fort Steele, near 7,000 feet elevation, Antares twinkled very much; and at Camp Douglas, 5,250 feet above the sea, the twinkling of several stars examined was surprisingly great.

At one point, however, he found the atmosphere without undulations, and the stars shone through it with a steady light. The central disk of Arcturus, he says, was hard and sharply defined; Antares near setting hardly twinkled at all; the moon was perfectly steady.

This point of observation was not far from Fort Steele, in the main range of the Rocky Mountains, at an elevation of 8,900 feet above the sea. Distant objects seemed near in the transparent air. The sky was not black, as he expected, but of a light blue; the moon, however, was near its full.

Another trial was made at Trout Lake, nearly 10,000 feet above the sea-level, and the air was found to be unsteady but transparent. At this point, however, intense cold, fierce winds, and heavy snow-falls, occur, making the location of an observatory here undesirable.

Dr. Draper concludes that the atmosphere in these high regions, although more transparent, is quite as tremulous as at the ocean-level at New York.

Influence of Heat on Galvanic Conductivity.—Till very recently it was held to be a law of Nature that the galvanic conductivity of all metals and metalloids is diminished by rise of temperature. It has been shown, however, that selenium is an exception to this rule, its conductivity being increased by heating. And now a further exception must be made in the case of tellurium, a body closely allied to selenium. We have already (in vol. x., p. 115) given an account of Siemens's researches on the action of light on selenium; we now present a synopsis of the results obtained by Franz Exner in his experiments with tellurium. Three bars of tellurium were prepared. Bar 1 broke before its dimensions were determined; bar 2 was 54 millimetres in length and 2.6 millimetres diameter; bar 3 was 153 millimetres in length and 3.73 millimetres diameter. Bar 1 was heated to 200°