Page:Popular Science Monthly Volume 19.djvu/583

Rh sent from Paris to Sir William Thomson at Glasgow, which was found by him to contain electrical energy equal to something over one million foot-pounds, or one-horse power, for one hour. Though the battery was seventy-two hours reaching him, it was -found to have lost but very little of its original charge, and he has since been able to detect but a slight loss in a period of ten days. The expectations regarding the uses to which this battery can be put are doubtless exaggerated, but it seems safe to predict for it a large field of usefulness. It can probably be employed to advantage, if further experiment bears out present statements regarding it, wherever ordinary batteries are used, as it possesses the convenience of these combined with the cheapness of the dynamo-machine in the matter of the currents furnished. In the electric light it will probably find an important use in equalizing the currents of the machines, and preventing interruption of the light in case of a temporary failure of the generating apparatus. It is, moreover, not impossible that it may dispense with the need for electrical distribution at all, as such batteries placed in houses could be charged each day by small dynamo-machines driven by gas engines, at but small expense and with the minimum amount of trouble.

Color-Blindness and Education of the Color-Sense.—The examinations instituted by Dr. B. Joy Jeffries among the pupils in the schools of Boston (including 14,469 boys and young men and 13,458 girls and young women) have shown that about one male person in twenty-five is color-blind, while the defect occurs with extreme rarity in girls and women (only 0·066 per cent, of the female pupils in the schools). The researches that have been made in Europe show that a similar law as to the relative proportion of color-blindness between the sexes prevails there. The subject has been overlooked until within a few years, but the value of the knowledge of it that has been gained can not be disputed. This knowledge can be applied practically on a scale of considerable extent in determining the vocation to which boys should be trained. A person who is color-blind is obviously unfit for any business in which he must know how to distinguish colors. Yet the person himself and those who are around him are seldom aware of his defect. If examinations are regularly made in the schools and records kept of them, as has been done by Professor Jeffries, a sure practical test may be found which can be applied directly to each person, so as to guide him aright on this point. The inquiries of Dr. Jeffries have disclosed a great lack of knowledge of colors, aside from color-blindness, among adults as well as among the boys in the schools. But very few boys of the grammar or higher schools, he says, are familiar with the color names of even the primary colors, and still less can they correctly apply those names they do remember, when shown colored objects. "I have received letters from adults, not color-blind, whose lack of color-names had been a serious drawback to them in their occupations in every-day life; and they have besought me to urge the teaching of color-names and the education of the color sense in our public schools." The teaching of colors and color-names has been partly introduced into our primary schools, but without any system; it has been begun in Europe, especially in Germany, in the lowest schools, in a systematic manner. The exemption of women from color-blindness has been attributed to their familiarity with colored objects and materials; but this holds only of the sex as a whole, not with reference to individuals, for the color-sense can not be changed with practice in colors. The question arises whether generations of color education have caused this sexual difference, and is important; for, if answered in the affirmative, it proves that we may begin to eliminate color-blindness from future generations of boys by teaching and exercising the present generation in the perception and distinction of colors.

Climate and Health.—Mr. Alexander William Mitchinson has read an important paper in the Society of Arts on "The Principal Causes of Disease in Tropical Countries." It is usual to trace these causes back to the climate, but Mr. Mitchinson maintains that climate has less to do directly in producing disease than has generally been supposed. Every climate and country has its own appropriate and dietary laws, and