86o 



THE POPULAR SCIENCE MONTHLY. 



random of the green and confusion colors. 

 In either case the clerk has only to set down 

 the numbers, which tell the story, and fur- 

 nish 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-blind- 

 ness. The reports of the examinations have 

 almost uniformly shown that 4 - 2 per cent 

 of the men are color-biiud. 



New Conditions affecting Life in France. 



31. A. Legoyt has continued his reviews 

 of the movement of population in France, 

 with a study of the vital statistics of the 

 nation for 18V 9. 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 con- 

 sumption of liquors distilled from grain 

 and the beet-roct, 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 lon- 

 gevity. A new cause of mortality worthy 

 of attention is the continued increase in the 

 prices of the necessaries of life, accom- 

 panied by a decrease in the rate of interest 

 on invested funds. The population de- 

 creased in 1879 in twenty-six departments, 

 most of which were in Southern France, 

 where distress was occasioned by the rav- 

 ages 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 mar- 

 riages, 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. Canaille 

 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 di- 

 rection opposite to that of the sun. M. Faye 

 at a subsequent sitting answered this sug- 

 gestion 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 repul- 

 sive 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 succes- 

 sively, 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 meteoro- 

 logical effects are masked by the more evi- 

 dent effects of solar radiation which are at 

 work during exactly the same period. Mul- 

 tiple 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. 



