426 



SCIENCE 



[N. S. Vol. XXXIII. No. 846 



2. " There is another way in which the fer- 

 tility of the soil can be maintained, viz., by 

 arranging a system of rotation and growing 

 each year a crop that is not injured by the 

 excreta of the preceding crop."— U. S. Farm- 

 ers' Bulletin (1906) 257, p. 21. 



3. " The soil is the one indestructible, im- 

 mutable asset that the nation possesses. It is 

 the one resource that can not be exhausted; 

 that can not be used up." — Bureau of Soils 

 Bulletin (1909) 55, p. 66. 



4. " Prom the modern conception of the 

 nature and purpose of the soil it is evident 

 that it can not wear out, that so far as the 

 mineral food is concerned it will continue 

 automatically to supply adequate quantities of 

 the mineral plant foods for crops." — Bureau 

 of Soils Bulletin (1909) 55, p. 79. 



If again we turn from theory to science, we 

 find at the Eothamsted Station in a four-year 

 rotation, including always a legume crop, that 

 the yield of turnips decreased from 10 tons in 

 1848 to less than 1 ton per acre as an average 

 for the last 20 years ; that the barley decreased 

 from 46 bushels in 1849 to 14 bushels as an 

 average for the last 20 years; that the clover 

 has decreased from 2.8 tons per acre in 1850 

 to less than one half -ton average since 1890; 

 and that the wheat produced 30 bushels in 

 1851, and 33 bushels average during the next 

 12 years, but only 24 bushels since 1890, and 

 20 bushels per acre since 1900. 



As an average of the last twenty years the 

 value of the four crops on the unfertilized 

 land at Eothamsted is $33.83 (from four 

 acres), but where the same crops were grown 

 on adjoining land to which mineral plant food 

 had been applied the average value is $76.83, 

 the increase being 140 per cent, above the cost 

 of the minerals. Let us thank God for 

 Eothamsted, and be grateful that agriculture 

 has some facts. 



Likewise at State College, a four-year rota- 

 tion, including clover, has been practised for 

 nearly thirty years, but as an average of two 

 consecutive 12-year periods the value of the 

 four crops (corn, oats, wheat and hay) de- 

 creased from $44.20 to $32.72; but where 

 mineral plant food was applied the crop 



yields averaged 49 per cent, above the unfer- 

 tilized yields. 



Both the teaching of science as applied to 

 agriculture and the practise of farming, in 

 America, have suffered and still suffer from 

 an insufficient accumulation of facts and 

 from an over-production of theories and con- 

 clusions. 



While famine is frequent in China and 

 Eussia and almost constant in India — the only 

 great populous agricultural countries compar- 

 able with the United States in necessary self- 

 dependence — and while the beautiful level 

 upland Leonardtovm loam soils of southern 

 Maryland, near the city of Washington, still 

 lie agriculturally abandoned, with only 80 

 pounds of total phosphorus and 500 pounds of 

 total calcium per million in the surface soil 

 (facts discoverable even in Bureau of Soils 

 Bulletin 54), shall we encourage the Whitney- 

 Cameron doctrine^ that it is never necessary 

 at any time to introduce fertilizing material 

 into any soil for the purpose of increasing the 

 amount of plant food in thai soil? 



\ Cyril G. Hopkins 



UkivEBSiTY OF Illinois 



BROWNIAN MOVEMENTS AND MOLECULAR REALITY 



To THE Editor op Science: I have recently 

 received a copy of Mr. F. Soddy's English 

 translation of Professor Jean Perrin's paper 

 on " Brownian Movements and Molecular 

 Reality." Its perusal recalls to mind some 

 ideas I have entertained for a number of years 

 relative to a general physical theory based on 

 very simple facts or principles. The earliest 

 record I have of these ideas is in a memo- 

 randum note of November 10, 1897. In a 

 letter of January 30, 1900, to Professor Peter 

 S. Michie, of the department of philosophy, 

 U. S. Military Academy, West Point, the ideas 

 referred to were outlined rather more clearly 

 and I also presented a brief statement of 

 them under date of August 11, 1900, to the 

 International Congress of Physics which was 

 held at Paris in connection with the Universal 



^ Hearings before tlie Committee on Agriculture 

 of the United States House of Representatives 

 (1908), page 446; or Ginn & Company's "Soil 

 Fertility and Permanent Agriculture," page 315. 



