August iiS, 1910] 



NATURE 



rliorpe's lecture on ants, with their bidden and unbidden 

 guests, and also by Prof. Sjostedt's narrative of the 

 Swedish expedition to Kilimanjaro. Able communications 

 were also received from Dr. Horn (Berlin), M. Bouvier 

 (Paris), M. Honrath (Budapest), and others. 



On .\ugust 5 Mr. Hewlett, of the Agricultural Research 

 Institute at Pusa, India, gave an excellent account, illus- 

 trated by numerous photographs, of the work of that most 

 useful institution; and M. Lahille (Buenos .\ires) discoursed 

 to an appreciative audience of the progress of economic 

 entomology in the .Argentine. The sectional programme 

 also contained, amongst others, contributions from Dr. 

 W. J. Holland (Pittsburg), Mr. H. Skinner (Philadelphia), 

 and Dr. Horn (Berlin) ; but the chief business of the day 

 consisted in the winding-up address of the president, Prof. 

 Lameere, and the selection of Oxford as the scene of the 

 next International Congress of Entomology, to be held in 

 1912, with Prof. Poulton, F.R.S., as president. 



The evening of .August 5 was devoted to a banquet at 

 the Taverne Royale, and on -August 6 M. Max, Burgo- 

 master of Brussels, entertained the members of the con- 

 gress at a grand reception in the Hotel de Ville. The 

 exhibition buildings were open to members throughout the 

 whole of the congress, and excursions were organised in 

 the course of the week to the Congo Museum, the 

 .Ardennes, the Field of Waterloo, and other places of 

 interest. The Brussels Museum of Natural History was 

 also visited, and its treasures described by members of the 

 staflf. 



The congress, as a whole, was an undoubted success. 

 .Any defect that may have been noticed in the arrange- 

 ments was probably due to the fact that, this being the 

 first occasion of the kind, there were no precedents to 

 guide those responsible for the administration. Some in- 

 convenience was suffered from the circumstance that the 

 Salle des Fetes was in request for other purposes, which 

 interfered to an appreciable extent with the scientific busi- 

 ness of the general and sectional meetings ; for this, how- 

 ever, compensation was found in the varied attractions of 

 the e.xhibition, free access to which, by the liberality of 

 authorities, was allowed to all members of the congress. 



It is satisfactory to be able to record that, of the 2q2 

 members, 67 were representatives of the United Kingdom, 

 its colonies and dependencies. The contributions made by 

 our countrymen to the scientific work of the congress may 

 fairly be said to have surpassed in extent and value those 

 of any other nation — a fact which is of good augury for 

 the future of entomological research within the borders of 

 the British Empire. 



THE FIFTH INTERNATIONAL CONGRESS OF 



PHOTOGRAPHY. 

 "T^HE International Congresses of Photography, the first 

 of which was held in Paris in 18S9, are arranged at 

 irregular intervals as opportunities offer or necessity 

 renders desirable, that representatives of all countries may 

 meet and discuss questions of general importance. It is 

 hoped by this means to avoid, or at least mitigate, the 

 confusion that results from variations in standards, nomen- 

 clature, and methods, especially when such variations are 

 due more to accident than intention. 



The fifth congress, whicli has just been held in Brussels, 

 was well supported, most of the European nations, as 

 well as America, being represented. More than eighty 

 communications were included in the programme, and 

 these were classified into three main sections : — (i) Scien- 

 tific questions ; photochemistry ; scientific appUcations of 

 photography. (2) Technique of photography ; artistic ques- 

 tions ; industrial applications of photography. (3) Photo- 

 graphic documentation and archives ; bibliography ; legisla- 

 tion. The proceedings of the congress will be published 

 in full in the report that will be issued in due time. 



Several of the communications were of the nature of 

 reports setting forth the present state of the section of 

 photographic work dealt with. Captain Th. J. Saconney 

 dealt with aerial photo-surveying. E. Deville gave details 

 concerning photo-surveying in Canada, from which we 

 learn that the extent of the region so surveyed is some- 

 what greater than the combined areas of Holland and 

 Belgium, the most interesting application of the method 



NO. 2129, VOL. 84] 



being its application =.n defining the frontier between' 

 Alaska and Canada, a district of lofty mountains. A 

 commission was given three years to report concerning 

 a frontier of one thousand kilometres in length, and as 

 only the short summer season of each year was available, 

 on account of the climatic conditions, other than a photo- 

 graphic method would have been impossible. A satis- 

 factory map was prepared from the three thousand photo- 

 graphs made. The photographic method of surveying 

 employed in Canada is eminently praclical, not excluding 

 other methods, so that it should be understood merely that 

 photography plays the most important part in it. 



Prof. Wilder D. Bancroft contributed a long report on 

 the photographic emulsion, and from the facts that he 

 has set in due order concludes that the silver bromide 

 grain is a complex of silver bromide, gelatine, and water> 

 and that " the process of ripening consists in changing the 

 composition of the silver bromide grain towards an un- 

 known, optimum concentration." He concludes, too, that 

 it seems theoretically possible to make an almost infinitely 

 fast plate having a very fine grain. Dr. R. Luther set 

 forth the various arguments concerning the nature of the 

 developable image, and J. Desalme reported on present 

 notions concerning the theory of development. The latter 

 considers that the electrolytic hypothesis affords a much' 

 better explanation of development than that based on a 

 reduction by a purely chemical process, that is, that a 

 developing solution contains an electrolyte and a depolariser 

 suitable to the positive ions produced. This explains the- 

 non-equivalence of the alkalies if substituted in the pro- 

 portion of their combining weights. 



The difiiculties of measuring the true opacity or 

 obstructive power of photographic plates were described by 

 F. F. Renwick, who stated that the apparent opacity of a 

 negative under any given conditions is the algebraic sunt 

 of several variable properties. These he classifies as the- 

 simple obstructing power, the diffracting power of small 

 particles and of the slightly rough surface of the film, the 

 increase in transmitted light when the incident light falls 

 obliquely on the surface, and the increase when the plate 

 being measured is placed close to a reflecting surface 

 if the difference between the readings with the negative 

 so placed, and when the negative is removed, is taken as 

 the opacity. He also criticised adversely the use of 

 acetylene flames as light standards unless many stringent 

 precautions are taken. The principles involved in attempt- 

 ing to measure the diffuse reflecting power of photographic 

 plates were enumerated by A. Callier and R. von Camven- 

 berghe, but they gave no practical details. Drs. Mees 

 and Sheppard described various improvements in acetylene- 

 burners when used as secondary light standards, to meet 

 objections that have been urged against earlier forms, and' 

 referred shortly to other standards. Dr. E. Goldberg 

 described an apparatus that he has devised (made by 

 Schmidt and Haensch, of Berlin) by means of which the 

 characteristic curve of a plate can be obtained without 

 the more or less tedious plotting generally done. From 

 the group of papers dealing with these branches of the- 

 subject, it is clear that the measurement of the densities 

 of photographic plates is a process still set about with 

 difiiculties and confusions, and that much work remains 

 to be done in this direction. 



Coming to the more technical branches of the subject, 

 we find that a great many widely different matters were 

 treated of. Prof. R. W. Wood described how to take 

 photographs with infra-red and ultra-violet lights. For 

 the infra-red he uses, as a screen, a very dense cobalt 

 glass with either a saturated solution of potassium 

 bichromate or a suitable red aniline dye, and, of course, 

 a suitably red-sensitised plate. Under such conditions 

 grass and trees in full sunshine appear snowy white and 

 the sky as black as midnight. .All shadows are very 

 black, as there is practically no light from the sky to- 

 illuminate them. For the ultra-violet photographs, quartz 

 lens were used coated with metallic silver to such an 

 extent that a brilliantly lighted window was barely visible 

 through them, and appeared of a deep violet colour. The 

 light transmitted was of wave-lengths from 3100 to 3250. 

 When photographed under these conditions, certain white 

 flowers (as phlox) and Chinese white (zinc oxide) appear 

 as if absolutely black, but ordinary landscapes do not 



