620 



NA TURE 



[October 27, 1923 



but 9. ". »3. 15. 17, 10, 21, 23. 25, 27. 29, 31. vA. ^1. 

 37, and 3«j ma>' be most probably assignee! to 

 34. 36. 44. 4**. 5". 50. 54. 54. f>o. f>4. 66. 66. 7- 

 and 80 respectively. (The results for elcnieni:j 34, 

 36, 50, 54, {uid 80 "are Aston 's.) If this be accepted, 

 it follows that the differences 41 and 43 belong to 

 element 82, because (o) the mass-number 201 app)ears 

 to be unstable (being the head of a series of unstable 

 mass-numbers 201, 157, 113, 73, and 33). and there- 

 fore 41 cannot be assigned to element 80; and (6) 

 because it is to be expected that element 82, like 66 

 and 50, has two odd isotopes. These are in conse- 

 quence 205 and 207. 



Of the six isotopes mentioned above, 206, 208, and 

 210 are end-products of radiojictive series; possibly 

 207 is also ; so that this analysis, if confirmed expen- 

 mentally, cannot by itself claim to dispose of^the 

 view^hat common lead may be of raf I inactive origin. 

 Hut neither does it necessarily snjjxirt it ; the matter 

 is still left open. 



It is not unlikely that the odd mass-number 205 

 is an isobare, because thallium (^ = 8i) is likely to 

 consist of mass-numbers 203 and 205, not only because 

 its atomic weight lies between these numbers but also 

 from the analysis in my last letter. Aston, by showing 

 that mercury has probably an isotope of 197, first 

 established the possibility of the existence of odd 

 isobares in the inactive elements, since it is very 

 probable that gold's principal isotope is 197 also. 

 But, in general, odd i.sobares are likely to be rare 

 among inactive elements, but not impossible, as I said. 

 Neodymium, dysprosium, and ytterbium were not 

 mentioned in my last letter. The chief isotopes of 

 the first of these appear to be 142, 144, 145, and 146, 

 possibly 148 and 150 also ; of the second, 160, 161, 

 162, 163, 164, and possibly 166; and of the third 172, 

 173. 174. 175. 176. and possibly 178. I should like 

 also to make a few minor alterations to previous 

 statements. Lanthanum is apparently not simple 

 but includes (possibly very little of) 137 ; gold is not 

 likely to have 199 ; holmium is mainly 165. Tellurium 

 should contain 122. But as I have now been able to 

 calculate simply both unstable mass-numbers and 

 even isobares, details are not of first importance. 



It is not asked that any of the mass-numbers of 

 this or of the previous letter should be accepted before 

 being disproved or confirmed by experiment. But 

 they are of interest as being "the most probable 

 numbers obtained by a simple and straightforward 

 consideration of the facts of radioactivity on the 

 reasonable assumptions stated. 



A. S. Russell. 

 Dr. Lee's Laboratory, Christ Church, 

 Oxford, October 13. 



I ments, and I have done luitl.ino i 



»w.r«« than arrange 

 ible account of 



Problems of Hydrone and Water : the Origin of 

 Electricity in Thunderstorms. 



Prof. Armstrong's friendly criticism (Nature, 

 October 13, p. 537) of my theory of the origin of 

 electricity m thunderstonns seems to neglect the 

 fact that my explanation of thunderstorms is based 

 entirely upon experimental and observational evidence. 

 If experiments can be said to prove anything, then 

 my work and the work of others has shown con- 

 clusively that: (fl) if there are ascending currents 

 exceeding 8 metres per second in the atmosphere, 

 there must be a great deal of breaking of rain drops ; 

 (6) every time a water drop breaks there is a separation 

 of electricity ; (c) the broken water drops retain a 

 positive charge ; (rf) the air attains a negative charge. 

 On the other hand, observations have shown that 

 there is a considerable excess of positive electricity 

 brought down by rain. These are all tangible facts 

 which any one can test by making the suitable experi- 



NO. 2817, VOL. I 12] 



m into such a form 



If phenomena of thun(i< its. 



Surely I*rof. Armstrong does not wish to S) 

 that all this work is wrong l)ccau.He it does no; 

 with his theory of hydrones. He cannot e- 

 neglect the evidence that electricit>' is 

 when drops break, f>ecause. according to his iheory, 11 

 appears more likely that electricity would be pro- 

 duced when drops combine. 



What alternative has he to offer to a theory which 

 has met with very wide .f <■ ? He ^ 



" Assuming that my interpr^ • correct, 



not the great rise m potenti.n 1 ' * : 



lightning have its origin in the 

 operation of minute drops charge, .-> „,, , - 

 source ? " This is very depressing, for it thro 

 back to where we were twenty v«;ir< n.^i m ■ 

 unknown " external source " of el< 

 ous ideas of the increase in the j 

 due to the coalescence of the droj) 



Meteorological Office. London. 



The Occurrence of Urease. 



Letters on the occurrence of urease are pimu'i m 

 Nature of August 11 and September 22. In the 

 former, Prof. Werner reports that he has found iir-- ■ 

 in all the leguminous nodular growths he has tt 



in the latter. Prof. Beijerinck descritxjs how he 



detected the enzyme in B. radicicola. Prof. Werner 

 writes : " So far as we have been able to ascertain, 

 the peculiar root nodules of leguminous plants have 

 not hitherto been tested for urease." 1 reproduce, 

 therefore, the following passage from an article on 

 " The Function of Hormones in regulating Meta- 

 bolism," by my son and myself, published in the 

 Annals of Botany, vol. xxv.. No. xcviii., April 191 1. 



" Lastly, we may refer to the nodular growths on 

 the roots of leguminous plants ; these are known to 

 be most essential to the proper growth of the plant 

 but their function is by no means clear ; it is well 

 known that they are the seat of bacteroids and it 

 may be that these function as assimilators of atmos- 

 pheric nitrogen gas and convert it into ammonia ; or 

 it may be that they exercise digestive functions and 

 serve to ' deamidate ' amino-compounds. At all 

 events, they are distinctly alkaline, whereas the root 

 sap is acid. Moreover, it has been shown by 

 Hutchinson and Miller, that, when distilled with 

 magnesia under reduced pressure, the nodules furnish 

 more ammonia than do the roots (0-043 per cent, 

 against 0016 per cent.). We suggest that some part 

 at least of the influence exercised by the nodules mav 

 be due to their aminogenetic power. We projxjse to 

 make this eissumption the basis of experimental 

 inquiry." 



Then, I would direct attention to the British 

 Association Report, Australia, 19 14, where, at p. 109, 

 the following passages are to be found, at the end of 

 the Report of the Committee for the Study of Plant 

 Enzymes. 



" In view of the presence of ammonia in the 

 nodular growths appearing on the roots of Legumi- 

 nosae, it appeared probable that the enzyme Urease 

 would be found in these. It has been detected in 

 the nodules from Lupins and a number of other 

 Leguminosae. Attempts to detect the enzj-me in 

 organisms cultivated from the nodules have thus far 

 been attended with negative results. 



" Mr. Benjamin, working at Hawkesbun.' Agricul- 

 tural College, near Sydney, Australia, has detected 

 urease in nodules from several Australian plants, 

 including wattles ; also on tubercles derived from the 



