13H 



KNOWLEDGE. 



June. 1911. 



technical work is available than was shown, and that when the 

 Section has become more familiar to Exhibitors much better 

 results may be expected. 



In Section 3, devoted to Colour- Photography, many 

 transparencies of scientific interest were shown. Professor 

 Waymouth Reid showed a splendid collection of Autochromes. 

 including a very large and fine polarised light figure of the 

 mineral Barytes.- Other polarisation colour-slides were shown 

 by Professor Pope. J. G. Bradbury and A. W. Harris. 



There is no doubt that for the demonstration of polarised 

 effects the .Autochrome plate will prove most suitable, and 

 should in the end win an important place for itself in the class 

 teaching of Mineralogy. 



Of Botanical work also there were many fine examples: 

 the Alpine flowers of Mr. Somerville Hastings being 

 conspicuous. 



Dr. Drake Brockman showed a number of moths and 

 butterflies, while Mr. Martin Duncan, Mr. J.I. Pigg and Mr. 

 P. C. Dalliriger, as well as Prof. Waymouth Reid, showed 

 photomicrographs in colour. 



As a whole the Colour Section must be considered excellent 

 in quality, and thoroughly representative of the valuable work 

 that can be done on screenplates. 



Of Natural History Photography the present writer is 

 scarcely competent to speak, but to an outsider the Section 

 seemed a good one. and many interesting photographs were 

 shown. 



Technicall}', Mr. H. C. Knowles' photograph of the (jreat 

 American Egret, reproduced in the Exhibition Catalogue, is 

 excellent work, while the Yawning J.aguar of Mr. H. Irving, 

 strikes a rather unusual note. Mr. C. J. King contributes a 

 series of patient studies of Peregrine Falcons, and indeed the 

 Section is unusually rich in series of photographs illustrating 

 the life-history of birds and beasts, in which perhaps the chief 

 scientific value of Natural History photography is to be found- 

 An excellent example was the series of twelve prints illustra. 

 ting the life-history of the Nightjar during the nesting period, 

 by Mr. William Farren. Mr. Pike's photograph of the 

 Gannet going down wind will appeal to most photographers 

 and makes one inclined to suggest that it might be an 

 improvement to this Section, even at the cost of enlarging the 

 Catalogue, if fuller particulars of the way in which the 

 photographs were taken were given. 



Section 5, which is devoted to Scientific Photography and 

 Reproduction Processes, was particularly strong this year, both 

 the Photoniicrographic and X-Ray sections being very represen- 

 tative. The Astronomical section, containing a large number 

 of very high-class transparencies, is liable to be somewhat 

 ignored by the general public. It would perhaps be better if 

 astronomical workers were to prepare prints from their negatives 

 for such an Exhibition, even though transparencies show more 

 detail and better render gradation. Transparencies are very 

 difficult to hang and light satisfactorily in an Exhibition, and 

 are therefore liable to be separated from the rest of the 

 scientific section, and to suffer in consequence. 



The first eight frames of the Scientific Section were a collec- 

 tion of examples of new methods of process reproduction shown 

 by the London County Council School of Photo-Engraving and 

 Litho.graphy ; they comprised frames showing the new Rotary 

 photogravure as applied to newspaper illustration, and also 

 the improvements in relief methods which the introduction of 

 intaglio processes has stimulated. There was also an excellent 

 frame showing Rotary photogravure in colour, and another 

 showing Photolithograpiiy in colour from half-tone transfers 

 printed by the oflf-set process. 



Immediately after these the photomicrographic section 

 commenced with a splendid series of high-power photo- 

 micrographs of diatoms by Dr. T. W. Butcher, which have 

 received a well-deserved medal. Conspicuous in this section 

 also were the pathological photomicrographs of Mr. Richard 

 Mnir. and the bacteria and trypanosomes of Dr. Duncan J. 

 Reid, an interesting frame. No. 633. by the latter giving full 

 particulars of the photographic conditions under which a 

 number of varying objects were taken. A careful studv of 



this frame could not f.iil to be of use to any worker in this 

 subject. 



Mr. C. R. Darling showed a series of photographs of drop 

 formation, the drops consisting of aniline oil suspended in 

 water. 



One of the best photographs, technically, in the whole 

 Exhibition was Jlr. H. N. Newton's photograph of a dissected 

 human heart. No. 653, which showed the ventricles and valves 

 with strengthening cords. .\ large number of photographs of 

 osmotic growths was shown by Dr. Stephane Leduc. and 

 others were contributed by Dr. J. Gray Duncanson. 



The Radiographic Section vied with that dealing with 

 Photomicrography in being fully representati\e and of the 

 highest order. The medal was given to Dr. Thurstan Holland 

 for his numerous photographs, and was no doubt awarded as 

 much for the general excellent work which Dr. Holland has done 

 in perfecting X-Ray technique as for the special photographs 

 shown at this Exhibition. As Dr. Holland also received a 

 medal for his photograph in Section 2, he is in the unusual 

 position of receiving two medals in the same Exhibition. 



Other excellent radiographs were shown by Dr. Robert Knox, 

 whose technical skill closely approaches that of Dr. Holland's, 

 and by Dr. G. H. Rodman ; while two photographs of the 

 highest class were sent by Dr. G. T. Haenisch. 



The Astronomical Section of the Exhibition was mainly 

 represented by the many transparencies shown by the Lowell 

 Obser\atory and b\- Dr. Max \\'olf of Heidelberg. Dr. Wolf 

 showed a collection of no less than 50 lantern slides, while 

 Lowell Observatory sent a series of photographs of Saturn 

 and Jupiter, and of Comet a 1910 and of Halley's Comet, the 

 spectrum of Halley's Comet being also shown. 



In Spectroscopy, Professor 2eeman received a medal for his 

 absorption lines of Sodium in a magnetic field, the resolution 

 being very clearly shown. The definition which can be 

 obtained in Spectroscopy under the best conditions was well 

 shown by Mr. Stanley in his enlarged photographs of the iron 

 and aluminium arc spectra. 



Many other interesting photographs were shown, but one 

 cannot help feeling that an Exhibition such as this might be 

 made much more fully representatix'e of the application of 

 photography to science, if scientific workers generally would 

 take more interest in it and endeavour to make use of the 

 opportunity of la\-ing their results before the general public. 



PHYSICS. 



By A. C. G. Egerton, B.Sc. 



OPTICAL PROPERTIES OF VAPOURS.— Professor 

 R. W. Wood has recently delivered three lectures at the 

 Royal Institution, on the optical properties of vapours. These 

 lectures were illustrated by experiments, illustrating most 

 beautifully the various phenomena referred to by the lecturer, 

 who is a master of the art of designing experiments and whose 

 ingenuity is unbounded. 



His first lecture dealt with the absorption of light by 

 vapours. Many substances have a definite colour in the 

 gaseous state ; nitrogen peroxide is brown, iodine vapour 

 violet, chlorine green, nitrosodimethylaniline green — a few of 

 many examples. If light, after passing through such gases, is 

 analysed bj- a spectroscope, the spectrum will be crossed by 

 dark lines and in some cases by dark bands. The light of 

 these wave-lengths corresponding to the dark lines and bands 

 has been absorbed by the vapour. In the same way the light 

 from the photosphere of the sun is absorbed by the layers of 

 vapour round the sun constituting its atmosphere : dark lines 

 then make their appearance in the sun's spectrum correspond- 

 ing to the elements in the state of vapour in the sun. At the 

 time of an eclipse, when the moon hides the sun's disc-like 

 form, the spectrum of the corona is often found to contain 

 bright lines in the neighbourhood of prominent absorption 

 bands in the solar spectrum, those about the yellow sodium 

 lines being peculiarly prominent. It was not easy to explain 

 how the " reversing " layer, or the layer of gas responsible for 

 the absorption of the light from the photosphere should be 

 hot enough to emit light of its own. This particular bright 



