284 



THE POPULAR SCIENCE MONTHLY. 



following result? : 1. That the oil- and gas- 

 lights, when shown through similar lenses 

 were equally affected by atmospheric varia- 

 tion; '1. That tin.' electric light is absorbed 

 more largely by haze and fog than either 

 the oil- or the gas-light; and, 3. That all 

 three are nearly equally affected by rain. 

 The final conclusions of the committee are 

 that for ordinary necessities of lighthouse 

 illumination mineral oil is the most simple 

 and economical illumir.ant ; and that for 

 salient headlands, important land-falls, and 

 places where a very powerful light is re- 

 quired, electricity offers the greatest advan- 

 tages. 



Heredity and Education, — "Heredity 

 and Education ; their Relation to Each Other 

 and to the Human Race," is the title of an 

 address by Dr. E. A. Wood, as President of 

 the Pennsylvania Medical Society. The au- 

 thor holds very positive views on the sub- 

 ject, both as to the excellence to which he 

 would have us aim to bring the race, and 

 with regard to the means to be used "to 

 reach the end. " If such a man as Shake- 

 speare," he asks, " has lived, why may not 

 men as great as he live again ; and if one 

 man attained this greatness, why may not 

 the average man ? If the old Greeks reached 

 such perfect development, why may not 

 Americans ? Is it possible that we have 

 reached the zenith of our possibilities ? Is 

 it not rather probable that Shakespeare ap- 

 proximated but did not attain the possible 

 average of human development ? . . . Na- 

 ture has written all over her page that New- 

 ton and Shakespeare were not accidents, 

 but advance heralds, proclaiming the coming 

 man. No man can conceive of the latent 

 potentiality of the human race ; by right 

 effort continued in the right direction, man 

 may be developed into a being grander than 

 his loftiest ideals." Further: "Let it be writ- 

 ten that many races of men have improved, 

 are improving, and bid fair still further to 

 improve; but man has not improved in ac- 

 cord with his powers and opportunities, has 

 not reached the Btandard of excellence 

 reached two thousand years ago, and is not 

 improving so rapidly as are the animals 

 i sated by him. The first step toward 

 race improvement must lie to teach our 

 children thai reproduction i- the highest 



and noblest function of the animal. We 

 are losing time by not teaching this lesson, 

 and all implied by it, immediately and thor- 

 oughly." 



The Future of the Snpply of Plant- 

 Food. — Vice-President Wiley began his ad- 

 dress before the Chemical Section of the 

 American Association — which was on "The 

 Economical Aspect of Agricultural Chemis- 

 try " — with a rough estimate of the money 

 value of the potash, phosphoric acid, and 

 nitrogen contained in a single harvest, the 

 total of which he placed at $3,343,786,050. 

 This seems to be an enormous quantity of 

 plant-food to be removed from the soil an- 

 nually, but it must be remembered that it 

 is not all lost ; much of it is left in the soil 

 in roots, straw, stalks, etc. But too often 

 the debris is got rid of as quickly as possi- 

 ble, and we have in practice not tilling but 

 killing the soil. The stores of plant-food 

 which have accumulated in our virgin soils 

 are indeed great, but they can not withstand 

 this constant drain vpon them. The pot- 

 ash that is in the soil may be estimated as 

 enough to last two hundred and fifty years, 

 and the phosphoric acid two hundred and 

 twenty-five years. Immense reserves of 

 both substances are, however, existent and 

 accessible — the potash in feldspathic rocks, 

 and phosphorus in the phosphate - beds. 

 Still, the exportation of agricultural prod- 

 ucts becomes a slow but certain method of 

 securing Eoil exhaustion. In point of fact, 

 however, Professor Wiley further showed, 

 the impoverishment of the soil takes place 

 at a much slower rate than the theory an- 

 nounced above would indicate. Doubth bs, 

 much reserve food is brought from the sub- 

 soil, and, if it be possible for the subterra- 

 nean stores of these materials to gradually 

 work their way surface-ward, even the re- 

 mote future need not fear a dearth of them. 

 There is also a certain conservatism in crops, 

 a vegetable " good breeding," which pre- 

 vents the growing plant from taking all the 

 food in sight. As long as there is abun- 

 dance, the plant is a hearty eater ; but, when 

 the visible quantity of food falls to a cer- 

 tain minimum, it remains for a long time 

 without any rapid diminution. Respecting 

 the nitrogenous food of plants, Professor 

 Wiley presented a series of studies from 



