Page:Popular Science Monthly Volume 12.djvu/132

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122
THE POPULAR SCIENCE MONTHLY.

tion, by taking deep and slow inspirations—say twelve or fifteen a minute. By this means the action of the heart will become slower and feebler, less blood is thrown into the brain, and very soon a quiet feeling, ending in sleep, is induced. As by a slight effort of the will any one may try this, we leave the question of its value to the test of actual experiment.

 

A New Optical Experiment.—Mr. William Terrill offers in Nature a new lecture experiment for proving the compound nature of white light. This method is to arrange seven lanterns so as to project their several circles of light side by side on a white screen, then to color each circle by introducing slides of glass stained to imitate the seven colors of the spectrum (the proper intensity of color being found by trial); in this way are produced seven circles on the screen, colored from red to violet, and arranged side by side. Then by turning the several lanterns, so that the projected circles exactly overlap each other, one circle of white light is obtained, proving that the seven colors together make white light. The same effect can be produced with five colors only, if properly selected; and even two, the ordinary cobalt-blue and deep orange, will nearly do. If these two be made to partially overlap, the effect is very striking.

 

Dallinger's Studies of Minute Animal Forms.—The Rev. W. H. Dallinger, whose researches into the origin and development of minute life-forms have earned for him a distinguished place in the world of science, in a communication to the Royal Institution of Great Britain, gives a brief historical sketch of his labors in this field. Ten years ago Mr. Dallinger determined to work out, by actual microscopic observation, the life-history of some of the lowly and minute organisms which occur in putrid infusions. After four years of preparation, he commenced his wink in conjunction with Dr. Drysdale, the plan needing two observers. Each set of observations was made continuous, so that nothing should have to be inferred. Very high powers were employed, and the largest adult objects examined were 11000 of an inch, the smallest 14000. Six forms altogether were selected, and their whole history was worked out. At first it was supposed that reproduction by fission was the usual method, but prolonged research showed that spores were produced. These were so small that a magnifying power of 5,000 diameters was needed to see them as they began to grow. The glairy fluid from which they developed seemed at first homogeneous, and it was only when growth set in that the spores became visible. All that could be learned about the origin of the glairy fluid was, that a monad larger than usual, and with a granulated aspect toward the flagellate end, would seize on one in the ordinary condition; the two would swim about together till the larger absorbed the smaller, and the two were fused together. A motionless spheroidal glossy speck was then all that could be seen. This speck was found to be a sac, and, after remaining still from ten to thirty-six hours, it burst, and the glairy fluid flowed out. The young spores that came into view in this were watched through to the adult condition. Bearing on the subject of spontaneous generation, this fact was learned, that, while a temperature of 140° Fahr. was sufficient to cause the death of adults, the spores were able to grow even after having been heated to 300° Fahr. for ten minutes. That there is no such thing as spontaneous generation of monads seems to Mr. Dallinger quite clear; and he is satisfied that, when bacteria are studied after the same manner, the same law will be found to hold good with them.

 

Influence of the Environment.—As a striking instance of the transformation effected in a race by changed conditions of life, Das Ausland quotes, from Khanikoff 's "Memoir on the Ethnography of Persia," some observations on a colony of Würtemberg which in 1816 settled in the trans-Caucasus country, near Tiflis. The original colonists, we are informed, were "singularly ugly," with broad, square countenances, blond or red hair, and blue eyes. The second generation showed some improvement; black hair and black eyes were no longer rare. The third generation was so entirely altered that their Würtemberg descent was no longer visible, for now black hair and