Page:Popular Science Monthly Volume 20.djvu/882

860 random of the green and confusion colors. In either case the clerk has only to set down the numbers, which tell the story, and furnish the medical man all the facts he needs for making up his judgment. The test is applied in precisely the same way by means of the other half of the stick for red-blindness. The reports of the examinations have almost uniformly shown that 4·2 per cent of the men are color-blind.

New Conditions affecting Life in France.—M. A. Legoyt has continued his reviews of the movement of population in France, with a study of the vital statistics of the nation for 1879. The population of the country continues to increase, but at a constantly diminishing rate. The hygienic condition of the people has been improved by the prevalence of greater ease in living, the spread of vaccination, and increased scientific exactness in the healing art; but new causes of mortality, incontestably grave, have been introduced. The chief of these is the excessive use of alcoholic drinks, signalized by the more general consumption of liquors distilled from grain and the beet-root, taking the place of wine, which is likely to increase if the ravages of the phylloxera continue. It is also marked by an increase of arrests for intoxication, of persons found dead, and of suicides, traceable to this cause. The number of suicides has almost quadrupled since 1827, while the population has increased only one-fifth. The growth of mental diseases is also detrimental to public health and longevity. A new cause of mortality worthy of attention is the continued increase in the prices of the necessaries of life, accompanied by a decrease in the rate of interest on invested funds. The population decreased in 1879 in twenty-six departments, most of which were in Southern France, where distress was occasioned by the ravages of the phylloxera. In details, the vital reports for 1879 show a slight increase of marriages, a few less births, a few more deaths, than were returned in 1878, and a decrease in the excess of births over deaths, which was already small enough. No direct regular relation is discoverable, either in France or in twelve other countries which are compared with it for this view, between the proportion, to the thousand, of marriages, births, and deaths. Generally, but not always, a greater number of marriages was followed by a greater number of births.

Theories of Comets' Tails.—M. Camille Flammarion suggested an inquiry at a recent session of the French Academy of Sciences, whether the perfect transparency of the tails of comets should not authorize us to believe that they are not material, but an electrical or other excitation of the ether produced by the mysterious star in a direction opposite to that of the sun. M. Faye at a subsequent sitting answered this suggestion with a material theory, to the effect that the sun appears to be endowed at the same time with two forms of action, one attractive, the other repulsive. The repulsive force is not proportional to the masses, like attraction, but to the surfaces, and therefore produces effects which are more marked as the matters on which it acts are less dense. It is not exercised through every kind of matter, like attraction, but may be enfeebled or arrested by the interposition of the slightest screen. It is not propagated instantaneously, as attraction is, but successively, like light and heat; hence its action upon a point in motion is not exercised in the same direction as attraction, although both forces emanate from the same star. Finally, this force varies inversely as the square of the distance, the same as light and heat. The repulsive force operates on the planets and their satellites as well as upon comets, but has escaped attention as to them, in consequence of their compactness. It operates also upon our globe, upon the limits of our atmosphere, but its meteorological effects are masked by the more evident effects of solar radiation which are at work during exactly the same period. Multiple tails to comets are not exceptional, as was till lately believed; that quality has been found to be more general as comets have been observed with more powerful instruments. The recent comet (b, 1881), it is true, seems to have but one tail; but that is because we are not far removed from the plane of its orbit, within which all the tails are included, so that they appear to us projected upon one another. For the same reason the tail of this comet appears straight.