828 



NATURE 



[February 24, 192 1 



melted. Later they substituted for this a specially 

 constructed composite anode which yielded the rays 

 without the necessity of external heating. 



Both these methods have been employed recently at 

 the Cavendish Laboratory to investigate the constitu- 

 tion of lithium, the rays produced being analysed by 

 Sir j. J. Thomson's "parabola" method which gives 

 ample resolving power for this element. 



Br means of the composite anode (G. P. Thomson, 

 Proc. Camb. Phil. Soc, vol. xx., p. 211, 1920) a 

 number of plates were taken showing in several cases 

 double parabolas corresponding to 6 and 7, but owing 

 to the fact that spurious doubling had occasionally 

 occurred, due to instrumental trouble, publication was 

 withheld. 



It has now been found possible to apply the 

 externally heated anode, employed by Dempster in 

 19 18 for potentials of about 1000 volts, to high potential 

 rays. This arrangement is used at very low pres- 

 sures, and under these conditions metallic rays only 

 appear to be produced. 



Exceedingly satisfactory parabolas corresponding to 

 lithium have' been obtained, a strong one at 7 and a 

 faint companion at 6 (Na = 23). The intensity of the 

 latter appears to correspond well with the accepted 

 atomic weight 6-94. 



The foregoing results appear to leave no doubt that 

 lithium is a complex element with isotopes of atomic 

 weights' 6 and 7. Of course, no accuracy can be 

 claimed for these figures until higher resolution has 

 been applied, but there seems no reason to doubt that 

 they are very nearlv whole numbers. 



F. W. Aston. 



G. P. Thomson. 

 Cavendish Laboratory, 



February. 



The Elementary Particle of Positive Electricity. 



The name "negative electron" was applied to the 

 elementary particle of negative electricity after the 

 experimental evidence for the variation of its mass 

 with velocity had generally convinced physicists that 

 its v.hole inertia was due to its electric charge. This 

 meaning of the term "electron" was in accord with 

 Dr. Johnstone Stoney's original use of the word to 

 denote the elementary unit of electric charge. With 

 the introduction of the principle of relativity it became 

 clear that the variation of mass with velocity was 

 no characteristic attribute of electrical inertia, and 

 that therefore we have no proof that the negative 

 electron's inertia is wholly electromagnetic in origin. 

 In fact, the investigations of Abraham, Webster, and 

 others have shown that there must be some mass 

 present other than that due to the electron's electric 

 field. If we abide by Dr. Stoney's original meaning of 

 the word, it is therefore more than doubtful whether 

 we are justified in calling this negatively electrified 

 particle of matter an electron. Nevertheless, the 

 term is now so well established in the literature that 

 ■we use "electron" to denote this elementary particle 

 regardless of our view concerning the origin of its 

 mass. 



The arguments for and against the electrical origin 

 of the mass apply in exactly the same manner to the 

 elementary particle of positive as to the correspond- 

 ing particle of negative electricity. If the negative 

 particle can legitimately be termed an "electron," 

 it is thus equally legitimate to apply the term to the 

 positive particle, since it likewise carries the funda- 

 mental unit of electric charge. Why not, therefore, 

 denote both these elementary particles by the same 

 generic term "electron," distinguishing the "posi- 



NO. 2678, VOL. 106] 



tive " from the "negative " electrons when necessary, 

 as several writers have long been accustomed to do? 



It seems to me that the application of a distinctive 

 name, such as "proton" or " hylon " or "hydrion," 

 to the elementary particle of positive electricity can 

 only suggest a distinction between the nature of the 

 positive and negative electrons, which, so far as we 

 are aware, does not exist. Thus, for example, when, 

 an atom of hydrogen is split into its two components 

 the negative electron is just as really a hydrogen ion 

 as is the positive electron. The fact that both com- 

 ponents possess equally fundamental units of electric 

 charge and are equally fundamental divisions of 

 matter should suggest that the same generic name 

 "electron " be applied to each. 



Arthur H. Compton. 



Washington University, 



St. Louis, U.S.A., 



January 25. 



The Peltier Effect and Low-Temperature Research. 



I SHOULD like to inquire whether the Peltier effect 

 has ever been considered as an aid to the production 

 of very low temperatures. I understand that the 

 lowest temperatures yet obtained are those produced 

 by Dr. H. K. Onnes, of Leyden, who, by reducing 

 the temperature of metals to that of liquid helium, 

 has got down to within less than 4° of the absolute 

 zero of temperature, or more than 450° below zero 

 Fahrenheit. Onnes, moreover, found that at such a 

 temperature pure metals lose practically all elec- 

 trical resistance and become nearly perfect conductors. 



The suggestion is to apply the Peltier effect, which 

 consists in an observed diminution in temperature 

 when an electric current is passed in a particular 

 direction through a thermo-couple to obtain still lower 

 temperatures. 



At ordinary temperatures, when the metals com- 

 posing the thermo-couple have appreciable resistance, 

 the Peltier effect is largely masked by the C^R heat 

 produced in the metals by the passage of the current. 

 At the temperatures attained by Onnes, when resist- 

 ance practically vanishes, this condition should not 

 obtain, with the result that the application of the 

 Peltier effect would appear to give possibilities of 

 obtaining materially lower temperatures than have 

 yet been reached. A. A. Campbell Swinton. 



66 Victoria Street, 



London, S.W.i, 



February 16. 



Heredity and Biological Terms. 



It seems to me that the arguments of Sir Archdall 

 Reid (Nature, February 3, p. 726) and Sir Bryan 

 Donkin (February 10, p. 75S) leave the question of 

 the meaning and use of the term " acquired charac- 

 ters " very much where it was before. Sir Bryan 

 Donkin asks whether it may not be justly argued 

 that if a child has a hand like its parent there is no 

 change in "nature" or "nurture"; that if the child 

 has a sixth digit which the parent had not there is a 

 change in nature or heritage, but none in nurture ; 

 and that if the child has a scar there is no change 

 in heritage, but only one in nurture. But I fail to 

 perceive anything new in this or any difference from 

 the usual conceptions which are general among bio- 

 logists. It is a mere matter of terms and synonyms. 

 The modern biologist would say that the normal 

 hand was hereditary, or innate, or due to certain 

 factors or genes in the chromosomes which usually 



