August 13, 1915] 



SCIENCE 



219 



sonable to demand a full presentation of her 

 data on the inheritance of albinism in mice. 

 In fact, a careful repetition of such work 

 should be expected before her claims are to 

 be accepted. 



To those unfamiliar with the work of the 

 geneticists above mentioned, Slye's paper might 

 be taken as presenting the well-known prin- 

 ciples of Mendelian inheritance. With a 

 knowledge of the facts, however, it is obvious 

 that the type of inheritance which she outlines 

 has not been observed in similar material by 

 any of the investigators above mentioned. 

 That this discrepancy is not based on an over- 

 sight on the part of Miss Slye has been deter- 

 mined by personal correspondence. 



C. C. Little 



Haevard University 



radidm peetilizer 



In a recent number of Science^ there ap- 

 peared an article by Hopkins and Sachs of the 

 University of Illinois on " Radium Fertilizer 

 in Field Tests " in which they gave results of a 

 series of tests where they used .01, .1 and 1 

 milligram of radium per acre. Their results 

 showed that radium used in these amounts had 

 no effect. 



It is well known that radium is present in all 

 substances in slight traces. I thought it of 

 interest to calculate the amount of radium in 

 one acre. The question immediately arises. 

 What is the volume of an acre? For agricul- 

 tural purposes I think that every one will agree 

 that the soil should be at least 5 inches, 12J 

 centimeters, deep. 



There are 43,560 square feet in one acre. 

 This when reduced to square centimeters is 

 approximately 40,000,000 or 4X10^. This 

 when multiplied by the depth, 12J is 5 X 10' 

 cubic centimeters. Taking Rutherford's aver- 

 age value for the amount of radium in the 

 crust of the earth as 2 X 10"^- grams radium 

 per gram of material,^ and calling the density 

 of the soil, which is about 1.2, unity, and then 

 multiplying 5 X 10^ by 2 X 10"^' we have 



1 Vol. 41, p. 732, May 14, 1915. 



2 "Rutherford Radioactive Substances and Their 

 Radiations," p. 650. 



1 X 10"^ grams or 1 milligram of radium in 

 an acre of soil. 



Thus Hopkins and Sachs in using their 

 maximum amount, 1 milligram, at a cost of 

 $100 only doubled the amount of radium in 

 the soil. A fertilizer is on the market which 

 contains radium, .05 to .08 microgram, or 5 

 to 8 X 10"^ grams to the pound. The company 

 recommends one pound of the fertilizer to fifty 

 square feet of soil. Fifty square feet of soil, 

 figured as above, contains about 5 X 10"' 

 grams of radium. Thus the average soil con- 

 tains ten times as much as they recommend in 

 their fertilizer. 



Besides the radium in the soil we have the 

 radium emanation, a gas which slowly rises 

 through the soil from the interior of the earth. 

 Experiments show that about 1,000 X 10"^^ 

 curies of radium emanation issue from every 

 square meter of the earth's surface in an hour. 

 (A curie of emanation is the amount of em- 

 anation which is in equilibrium with one gram 

 of radium, or the amount which will collect 

 in a closed vessel in 30 days when the vessel 

 contains one gram of radium.) Every square 

 centimeter of the earth's surface gives off 

 .1X10"'- curies per hour, or .0003X10"'^ 

 curies per second. One curie equals about 

 4.8 X 10^ gram seconds. (A gram second is 

 the amount of radium emanation given off by 

 a gram of radium in a second.) Then 

 .0003X10-'- curies equals about 150X10"'=' 

 gram seconds, or the amount of radium em- 

 anation which is continually given off by 

 150 X 10"'- grams of radium. 



Thus the amount of radium emanation given 

 off by the soil is 50 to 100 times as much as 

 that which is given off by the radium in the 

 upper five-inch layer of the soil. 



To double the emanation in the soil one 

 must use about 75 milligrams of radium per 

 acre at a cost of $7,500 per acre. 



R. R. Ramsey 



Department op Physics, 

 Indiana University 



sugar-beet mosaic 

 Although this disease of the sugar beet has 

 been observed for more than a dozen years it 



