August 4, 1923] 



NA TURE 



i»i 



although, if the intermediate stages are those which 

 are conventionally postulated, the optical activity 

 must necessarily disappear, since the intermediate 

 product would be symmetrical. The preservation 

 of asymmetry can, however, be explained by means 

 of partial valencies, through which the asymmetry of 

 one atom is maintained until it has been stabilised 

 again either in the same atoin or in a different one. 



The bearing of the theory of polarity on the re- 

 activity of organic compounds was discussed by Mr-. 

 E. K. Rideal, and, as illustrating this aspect of the 

 problem, ]Mr. R. G. W. Norrish described some 

 experiments which he has jvist carried out, according 

 to which the union of ethylene and bromine is almost 

 stopped by enclosing the mixed gases in a vessel 

 lined with parafhn wax, whereas in contact with the 

 polar surface of a glass vessel combination takes 

 place rapidly. 



In the general discussion, to which about a dozen 

 different speakers contributed, Prof. J. F. Thorpe 

 urged that the theory of polarity " explains every- 

 thing but predicts nothing," in marked contrast to 

 van 't Hoff's stereochemistry, which made organic 

 chemistry into the most exact of all the sciences. 

 This contention was strenuously denied by Mr. 

 Burkhardt from the Manchester laboratory and by 

 Profs. Noyes, Lapworth, Heilbron, and Robinson, 

 who proceeded to put on record two definite pre- 

 dictions in order to get over the difficulty that under 

 normal conditions the prediction and the verification 

 are published together, so that the reader cannot be 

 quite certain which really came first. Dr. Fliirscheim 

 also replied in a very vigorous manner to the criti- 

 cisms by Prof. Lowry of his views in reference to the 

 influence of substitution on the strength of carboxylic 

 acids, and urged that in several examples the forma- 

 tion of internal salts, which had been suggested as an 



alternative explanation by Prof. Lowry, cannot in 

 . fact take place. Prof. Lewis directed attention to 

 the fact that the breaking of a double bond does not 

 necessarily get rid of cis and trans isomerism, even 

 if free rotation can take place ; and in support of 

 this view Mr. Bury quoted the fact that quadrivalent 

 sulphur compounds retain their optical activity even 

 when one of the four groups is ionised. 



In the final session of the conference. Prof. Victor 

 Henri presented a paper on " Molecular Polarity 

 deduced from the Study of Absorption Spectra." 

 This proved to be a most remarkable contribution, 

 in which the application of considerations based on 

 the quantum theory led to the conclusion that 

 quantified motion may occur in electrons, atoms, or 

 molecules, giving rise to broad absorption-bands, 

 narrow absorption-bands, and a fine structure of 

 these bands, respectively. By making use of a 

 source of continuous ultra-violet light. Prof. Henri 

 has been able to study the fine structure of the 

 absorption bands of a large number of compounds, 

 and in some instances to measure as many as two 

 thousand bands in the fine structure. A large 

 number of photographs were shown to illustrate the 

 various types of absorption spectra. Prof. Henri's 

 paper produced a very profound impression by the 

 masterly character both of the theory and of the 

 experiments which he described. It may well mark 

 a new era in the history of absorption spectra. In 

 apologising to Prof. Henri for the fact that the late 

 hour did not allow of an opportunity for discussion, 

 the president added that the question of holding a 

 general discussion on absorption spectra is already 

 under consideration by the council of the Faraday 

 Society, and that such a discussion would allow of a 

 fuller consideration of the view which Prof. Henri 

 had put forward. 



International Conference of Phytopathology and Economic Entomology. 



T^HE first International Conference of Phytopatho- 

 ^ logy and Economic Entomology was held in 

 Holland on June 24-July 2 by the kind invitation of 

 the Netherlands Government in co-operation with the 

 authorities of the various laboratories and institutes 

 conducting work on agricultural phytopathology and 

 entomology. The Conference was noteworthy as 

 being the first occasion on which phytopathologists 

 and entomologists from all countries have been 

 invited to meet together to discuss matters of mutual 

 interest. Prof. H. M. Quanjer of Wageningen, pre- 

 sided over the Conference, while Dr. L. O. Howard, 

 Chief of the United States Bureau of Entomology, 

 acted as president of honour. Upwards of 65 members 

 attended — in addition to the Dutch participants — 

 representing some 26 countries. A report of the 

 Conference, giving an account of the demonstrations, 

 papers read, etc., will be issued by the Committee 

 of Management (obtainable from the Secretary, Mr. 

 T. A. C. Schoevers, of the Netherlands Phyto- 

 pathological Service, Wageningen), but in the 

 meantime the following brief account may be of 

 interest. 



Members assembled at Wageningen on June 24, 

 when an address of welcome was delivered by Prof. 

 Kielstra, Rector Magnificus of the University. On 

 the following morning the Conference was formally 

 opened by H.E. the Minister for Home Affairs and 

 Agriculture, and during the day members attended 

 the inauguration, by Jonkheer van Citters, of the 

 new Laboratory for Potato Research in which Prof. 



NO. 2805, VOL. I 12] 



Quanjer's Department is now housed. In the 

 laboratory and adjoining experiment station ex- 

 periments of great interest, notably in connexion 

 with the " virus " diseases of the potato, were in- 

 spected. After spending two days in conference, the 

 members divided into two parties, one visiting 

 Groningen and the other Boskoop, Aalsmeer and 

 Haarlem. The first party inspected the practical 

 application of Prof. Quanjer's experiments in the 

 selection fields and farm of Dr. O. Botjes, who 

 demonstrated his methods of obtaining "seed" 

 potatoes on a large scale entirely free from virus 

 diseases, and the second visited nurseries producing 

 ornamental plants, shrubs and bulbs ; at Lisse (near 

 Haarlem) they visited Dr. van Slogteren's new 

 laboratory for the study of bulb diseases, and were 

 treated to an excellent address and to demonstrations. 

 The two parties combined forces again at the laboratory 

 of Prof. Westerdijk, Director of the W. C. Scholten 

 Phytopathological Laboratory at Baarn, where the 

 final papers were read and the discussions concluded. 

 Subsequently H.E. the Minister for Home Affairs and 

 Agriculture held a farewell reception at the Hague, 

 and members were entertained to dinner at Scheven- 

 ingen. Many members remained until the following 

 week to take part in an expedition to the glass house 

 district of the Westland. 



Within a short space it is impossible to do justice 

 to the 'papers read. Two subjects were, however, 

 specially prominent — namely, (i) the research, both 

 botanical and entomological, which centres round the 



