October, 1913. 



KNOWLEDGE. 



391 



Figure 412. 



As will be observed in some of the illustrations, the flesh 

 parts and even the details of the muscles are apparent and are 

 clearly represented. It would be too long to enumerate the 

 applications which the new field of radio-micrography is 

 likely to obtain in the near future, but in furnishing the present 

 radiographs M. Goby is confident that scientific men will find it 

 valuable for different kinds of research work, and no doubt it 

 will be taken up in various quarters. Franc]s p> Mann _ 



Since the above was received M. Goby has described his 

 apparatus, and the following description is taken from a 

 translation of the contri- 

 bution to Compt es 

 Rendus, CLVI., pages 

 686-688, which appears 

 in the current number of 

 The Journal of the 

 Royal Microscopical 

 Society, from which 

 we have copied the 

 diagrams shown in 

 Figures 412 and 413. 



The difficulty of obtain- 

 ing by the Rontgen rays 

 the requisite clearness of 

 detail has been overcome 

 by means of the appar- 

 atus shown in Figure 413, 

 which is carried on the 

 telescopic pillar u v, the 

 movable joint s of which 

 allows it to be pivoted 

 in a horizontal position. 



Two large metal cylin- 

 ders a 1 , a 2 , the one sliding 



within the other, form a photographic camera body, the 

 length of which can be varied as wanted. The top of this 

 body c is provided with a socket c 1 through 

 which slides the axial metal tube d, which is 

 destined for suppression of the secondary or 

 superfluous rays, and for the transmission of the 

 cluster of active rays, which the thick leaden 

 diaphragm / of very small diameter allows to 

 pass, whilst a disc g opaque to the luminous rays 

 alone, shuts off other light which might affect the 

 photographic plate. 



At the other extremity of the tube d an 

 " incidence indicator " or device for enabling the 

 incidence of the rays to be regulated is adapted, 

 which consists essentially of a very narrow 

 metallic tube i, supported by two discs h 1 , h", 

 permeable to the X-rays. Normally to this is 

 placed a small fluorescent screen /, which can 

 be examined through a darkened glass disc k, 

 destined to protect the eye of the operator, 

 when the apparatus is put in a horizontal 

 position. By means of the mechanism o, p, q, 

 the focus tube carrier I can be adjusted in two 

 directions, and all that is necessary is to adjust 

 the special Rontgen tubes held by the isolating 

 clamps m, m 1 , so that the small luminous spot 

 is seen in the centre of the screen surrounded by 

 a dark circle, thus indicating that the central ray of the cluster 

 is following a path axial to the tube itself. One can now 

 regulate the desired sizes of the radiographic field indicated by 

 the extent of the illuminated zone of the screen, by sliding the 

 tube d nearer or farther away from the source of radiation. 

 After once centring the focus-tube by means of the incidence 

 indicator, this does not need to be repeated, the indicator 

 being then slipped out of the tube d and laid aside. 



All that now has to be done is, in the light of an ordinary 

 dark room, to place a small photographic plate, square by 

 preference and of very fine grain, on the centre of the leaden 

 disc 6, which forms the base of the camera, and which is 

 marked with a diametrical cross for purposes of registration. 

 The small object to be radiographed is placed in direct contact 



with the sensitised surface of the plate without the interposi- 

 tion of black paper. It only remains to pull down the 

 cylindrical camera body into its grove and to allow the 

 appropriate rays of a Rontgen tube, with a very small anti- 

 cathode, to act for a convenient time in order to obtain, thanks 

 to the normality of the incident rays and to the suppression 

 of the paper envelope, the great clearness of detail which 

 allows of the radio-micrographs being enlarged to a consider- 

 able size. 



PHOTOGRAPHY. 



By Edgar Senior. 



FAULTY PERSPECTIVE SEEN IN MANY 

 PHOTOGRAPHS. — Anyone who has compared a 

 photograph with the scene that it was intended to 

 represent must have noticed on many occasions 

 the great amount of difference existing between 

 the two with regard to the relative size of the 

 objects depicted when the photograph has been 

 taken with a short-focus lens. We have an 

 example before us as we write, taken with a lens 

 of this kind, in which the size of the objects in 

 the foreground is out of all proportion to those 

 at a distance, and this is by no means an isolated 

 example, but is quite a common effect obtained 

 by the use of wide-angle or short-focus lenses ; 

 and although wide-angle lenses are useful at 

 times, such as when working in confined situations, 

 there is the attendant disadvantage that objects 

 situated in the foreground are made to appear too 

 large compared with those at a distance. In con- 

 sidering the cause of this phenomenon, we must 

 remember that the eye when looking steadily at 

 an object forms an image upon the retina which embraces an 

 angle of not more than 60° ; therefore, in order that a 



photograph may convey a 

 correct idea of the 

 relative size of the objects 

 represented when it is 

 viewed at a distance of 

 ten or twelve inches, the 

 angle included in the 

 picture should not be 

 greater than that of the 

 angle it subtends for 

 vision, which is from 55° 

 to 60° ; since if more is 

 included in the photo- 

 graph than this, the 

 images of objects in the 

 foreground will appear 

 too large in comparison 

 with those at a distance. 

 To render it obvious that 

 distortion of this nature 

 is not really due to any 

 fault of the lens, it is 

 only necessary to view 

 the photograph at a 

 distance equal to the 

 focus of the lens with which it was taken for the distortion to 

 disappear, or, better still, to enlarge the picture, as then it would 

 be viewed at a correspondingly greater distance. The conditions 

 under which a photograph will give a true representation of 

 natural objects have received considerable attention from Dr. 

 Alexander Gleichen, and in a paper translated by Dr. Lindsay 

 Johnson, M.A., F.R.P.S., and published in The Photographic 

 Journal, the author appears to consider that the aperture of 

 the lens should not in any case be larger in diameter than the 

 pupil of the eye (about eight millimetres), and that the focus 

 of the lens employed should not be less than ten inches (the 

 normal distance of distinct vision), or if the focus is less 

 than this the picture must be afterwards enlarged as many 

 times as the focus is less. Now, in using a ten-inch 



^g^^^^^^^^K*^ 



Figure 413. 



