August 25, 1923] 



NA rURE 



289 



Current Topics and Events. 



Atomic projectiles have been used by many 

 investigators to batter down the defences which 

 have guarded so well the innermost mysteries of 

 the structure of matter. The a-particle, liberated 

 spontaneously in radioactive transformations, has, 

 thanks to its enormous velocity, been of special 

 service in elucidating the constitution of the atom. 

 In these investigations no one has played a more 

 important part than Sir Ernest Rutherford, and it is, 

 therefore, appropriate that in the address which 

 appears as a supplement to this issue of Nature 

 he should give an account of the life history of such 

 a high-speed a-particle. When the particle is ex- 

 pelled from a radioactive substance, it has been 

 proved to be the nucleus of a helium atom of mass 4 

 carrying two positive charges of electricity. Recent 

 experiments by Henderson have shown how, by the 

 successive capture of electrons, the a-particle becomes 

 a neutral helium atom. The experiments, which 

 were carried out by observing the deflexion of a 

 narrow pencil of a-rays in a magnetic field, have 

 been confirmed and extended by Sir Ernest Ruther- 

 ford. It appears that not only may the doubly 

 charged helium nucleus remove and capture an 

 electron from the outer electron structure of the 

 atoms in its path, but the converse change may also 

 take place. In passing through other atoms this 

 electron may be knocked off, and the singly charged 

 a-particle revert back to the doubly charged type. 

 The somewhat unexpected conclusion is reached 

 that this process of capture and loss may repeat 

 itself more than a thousand times in the flight of 

 the particle. Similar considerations apply in the 

 case of singly charged and neutral helium particles. 

 Though the results of these encounters may be less 

 startling than those in which disintegration of an 

 atomic nucleus like that of nitrogen or of aluminium 

 occurs, it seems probable that the study of these 

 rapid interchanges of charge will yield information 

 of great value to the theoretical physicist. 



The attempt to restrict the spread of epidemic 

 disease amongst plants is creating a phytopathological 

 service of inspection in many countries, and legislation 

 is gradually restricting the free movements of plants 

 and plant produce in and out of the various countries. 

 In a paper under the title " The Biological Basis of 

 Plant Quarantines " contributed to Phytopathology 

 for June, W. A. Orton and R. Kent Beattie attempt 

 to get down to the first principles underlying such 

 legislation, and their views deserve careful study in 

 Great Britain, both by growers and students of 

 pathology, as, if the conclusions arrived at find 

 favour in the United States, the British exporter of 

 plants may experience increasing difficulties in the way 

 of export trade with that country. The authors 

 draw a fundamental distinction between communica- 

 tions between countries that are close neighbours, 

 and traffic in plants across the ocean barriers that 

 separate continents. They conclude that within the 

 area of a continent the cultivated host plants and 

 their parasites will in most cases have fought out 



NO. 2808, VOL. 112] 



their battle and arrived at an approximate equi- 

 librium, the issue of the conflict varying of course 

 each season, but without violent fluctuation. When, 

 however, a parasite crosses an ocean barrier, then its 

 arrival in the new continent may be followed by 

 incalculable results, and a cultivated crop may almost 

 be exterminated before selection of more resistant 

 forms, or other factors operating over a space of time, 

 have again produced an equilibrium in which the 

 cultivation of the crop is economically possible, 

 allowing for the average loss produced by this parasite. 

 These results may follow, even when the parasite 

 thus introduced is one regarded as relatively in- 

 nocuous in the continent where it has long been 

 known. For example, chestnut bark disease, 

 Endothia parasitica, though a relatively minor 

 trouble in Asia, has, since its introduction to America, 

 bid fair to destroy all the chestnut forests of the 

 country. The author's arguments bring them into 

 disagreement with the conclusion of the last Inter- 

 national Phytopathological Convention, held in 

 Rome in 1914, as they emphasise the importance of 

 " common species of long-standing dispersion " which 

 inspecting officials naturally tend to overlook, and 

 lead them to the very important general principle 

 that " inter-continental trade in plant propagating 

 material is fundamentally dangerous, and to be held 

 within the narrowest limits compatible with economic 

 need." 



One of the best-known German scientific workers, 

 and at the same time one of the founders of modern 

 physical chemistry, Wilhelm Ostwald, who was born 

 September 2, 1853, at Riga, is about to celebrate his 

 seventieth birthday. After having studied at Dorpat 

 he was appointed, in 1883, professor of chemistry at 

 the Baltic Polytechnical School of Riga, and, in 1887, 

 professor of physical chemistry in Leipzig. Here he 

 developed a great ability as an investigator as well 

 as a teacher. His work gave a firm experimental 

 foundation to the theories of van 't Hoff and Sv. 

 Arrhenius. There, scientific workers from all over 

 the world assembled round the master, and built 

 up, in a short time, the edifice of modern physical 

 chemistry. Besides this work, Ostwald produced a 

 number of valuable text-books, including his large 

 " Outlines of General Chemistry," " The Fundamental 

 Principles of Chemistry," " The Principles of In- 

 organic Chemistry," and " Scientific Foundations of 

 Analytical Chemistry." At the end of last century 

 Ostwald devoted himself more to questions of natural 

 philosophy, such as the energy resources of the world. 

 These studies, the fight against scientific materialism, 

 and the propagation of Haeckel's monistic philosophy 

 so occupied his mind that he gave up his professorial 

 duties in 1906 and retired to his country seat in 

 Grossbothen, Saxony. It was a token of the breadth 

 and productivity of Ostwald's mind that even then 

 he created for himself quite a new sphere of activity. 

 Starting from the art of painting, which he had loved 

 and cultivated since his youth, he worked out a 

 new system of colour, by which every tint can be 



