March 19, 1920] 



SCIENCE 



291 



weights 35 and 37 for chlorine, thus confirm- 

 ing to this extent my theory with respect to 

 the light elements and also for the heavy 

 elements. Also in accord with the theory pre- 

 sented in my papers on atomic weights, he 

 finds that the atomic weights on the oxygen 

 basis are practically whole numbers. 



The details of our experimental work on 

 the separation of chlorine will be published as 

 soon as we have collected enough material to 

 enable us to make a more careful purification 

 of our material, and when in addition the 

 accurate atomic weight determinations have 

 been completed. "We expect to make the final 

 separations by thermal diffusion. The theory 

 of this method has been worked out by Chap- 

 man. Mr. Broeker and I are also beginning 

 preparations for an extensive attempt to 

 separate hydrogen into hydrogen and meta- 

 hydrogen, the latter with an atomic weight 

 of 3.0. While there was sufficient evidence 

 for the existence of a meta-chlorine in 

 ordinary chlorine to be found already in 

 the atomic weights, there is no such evi- 

 dence that ordinary hydrogen contains meta- 

 hydrogen. However, there is evidence that 

 the meta-hydrogen nucleus of a formula 

 /igg,*, where h is the hydrogen nucleus 

 and e is the negative electron, is the most 

 important unit in the building of atomic 

 nuclei, with the exception of the alpha 

 particle (h^Br,**). The nucleus of an isotopic 

 atom of higher atomic weight differs from the 

 nucleus of the normal atom by the presence 

 of a mu group (/loB,) which carries no net 

 charge, and which, if it were alone, would 

 have an atomic number zero. Isotopes of 

 higher atomic weight are also formed by the 

 addition of alpha groups (h^e^**), each alpha 

 group being attached by two cementing elec- 

 trons. This is equivalent to the addition of 

 an h^e^ group. The details of this system 

 will be found in a paper now in print in the 

 Physical Review. 



It should have been noted in the above 

 paper that neon, magnesium, and silicon, the 

 even nimibered light elements which contain 

 isotopes, lie adjacent in the even numbered 

 series, since their nimibers are 10, 12, and 14. 



It is possille that a third isotope of chlorine 

 exists. 



WiLLUM D. Harkins 

 Univeesitt op Chicago, 

 February 28, 1920 



WILHELM PFEFFER 



WiLHELM Pfeffer, with Sachs the founder 

 of plant-physiology as it has been studied for 

 more than a generation, died in Leipzig on 

 January 31, of this year. A long line of 

 Americans, as well as many other foreigners, 

 resorted to him, in addition to the Germans 

 who studied with him. He probably shared 

 with Strasburger the distinction of having a 

 larger number of foreign students of botany 

 than any other German university professor. 

 By these men, and many others, he will be re- 

 membered as a striking personality as well as 

 a great leader in the science to which he de- 

 voted his life. 



The details of his life are probably known 

 to few Americans, but the general outlines 

 may well be set down. He was born March 9, 

 1845, in Grebenstein near Cassel, the son of 

 an apothecary. The elements of science, and 

 scientific curiosity, he probably acquired from 

 his father ; for the old-time German Apotheker 

 was a very different sort of person from the 

 American drug-store proprietor of to-day. He 

 studied at the universities in Gottingen, Mar- 

 burg, Berlin and Wiirzburg, taking his doctor's 

 degree at Gottingen in 1865. He began his 

 teaching career as Privatdocent in Marburg, 

 going thence as Ausserordentlicher to Bonn 

 and as Ordentlicher Professor to Basel, Switz- 

 erland. In 1878 he removed to Tiibingen 

 where, I believe, the first Americans worked 

 with him, Goodale of Harvard, Wilson of Phil- 

 adelphia, Campbell of Stanford, and perhaps 

 others. In 1887 he went to Leipzig, where he 

 stayed for the rest of his life, in spite of calls 

 to what, to others, might have seemed more 

 attractive posts. But in the Botanisches In- 

 istitut in Leipzig he had a laboratory fitted to 

 his ideas and desires, with a garden adjacent 

 in which the material which he and his associ- 

 ates used could be readily grown, a garden of 

 such size, position, and plan that it took the 



