3<5 



NA TURE 



May 14, 1896 



THE ROYAL SOCIETY CONVERSAZIONE. 



F'ICW conversaziones of the Royal Society have exceeded in 

 interest tlie one held on Wednesday of last week. Many 

 of the exhibits were very striking, while all of them presented 

 novel features. Physical science predominated, and Kcintgen 

 jjhotography attracted a large share of attention throughout the 

 ■evening. .Mr. A. A. C. Swinton had an elaborate exhibit to 

 illustrate experimentally the production of Riintgen lays, and 

 the visible ami (ihotographic effects produced Ijy them. By 

 means of several binocular cryptoscopes, all who so desired were 

 able to see shadow pictures of the bones in the living body, 

 and of objects enclosed in opaque boxes, while Rdntgen photo- 

 graphs of the hands of many persons were taken during the 

 evening. 



Mr. Herbert Jackson's demonstration of the use of phos- 

 phorescent materials in rendering Rontgen rays visible, brought 

 ■out the supremacy of potassium platino-cyanide as the salt for 

 phosphorescent screens. The tul)e used to produce the rays 

 was a slight modification (described in the Proceedings of the 

 Chemical Society) of a tube originally introduced by Mr. 

 Crookes to illustrate the heating effect of kathode rays. These 

 are brought to a focus at the centre of curvature of the concave 

 kathode, whence they proceed in nearly a straight line to a 

 platinum plate, from the surface of which they are apparently 

 scattered in all directions. The rays penetrating the glass were 

 caused to fall upon phosphorescent bodies and were rendered 

 visible, thus .showing the different intensities of response of these 

 bodies to such rays. By means of a large phosphorescent screen 

 covered with platino-cyanide of potassium, all the efiects seen 

 individually with a cryptoscope were viewed by a number of 

 people at the same time. 



Mr. Sydney Rowland exhibited a series of "skiagrams" 

 illustrating the applications of the "new photography" to 

 medical and surgical diagnosis. The following analysis, based 

 ■on a record of some fifty cases, is useful as showing the branches 

 of surgery in which the new process will probably be found of 

 most use. About 20 per cent, of these include the discovery 

 ■ana location of foreign bodies, needles, bullets, &c., lodged in 

 soft tissues, and in one case a coin lodged in the intestine, 

 which caused Irouljlesome symptoms. In one of these cases 

 ■two previous operations had been fruitlessly performed. 15 per 

 ■cent, of the cases were instances of pathological conditions of 

 the elbow-joint of more or less obscurity, on which new and 

 imexpected light was thrown by the diagnosis thus obtained. 

 In 10 per cent, of the cases the object in view was the deter- 

 mination of the extent and distribution of tuberculous lesions in 

 bone. Various ankyloses and deformities of the bones and joints 

 of the extremities have made up the remainder of the cases. 



A self-testing resistance box and bridge were exhibited by 

 Mr. E. H. Griffiths, F.R.S. This apparatus presented many 

 novel features, the chief advantages being as follows : — ( i ) The 

 ■observer can (without use of standards, ike] ascertain accurately, 

 .and quickly, the comparative errors of all the coils, including 

 those in the ratio-arms. (2) An exact calibration of the bridge 

 wire can be made Ijy means of the box itself. (3) The tem- 

 perature of the coils can be accurately determined. (4) The 

 .resistance of leads to any object is self-eliminated. (5) Resist- 

 ances from o'ooooi ohm to 105 ohms can be directly read by a 

 null method, without observation of galvanometer swings. (6) 

 All coils after adjustment have been heated to a red heat, and 

 .are thus very free from strain, &c. (7) There are special arrange- 

 ments for securing constancy of all plug contacts, &c. 



A resistance box, standard coils, and wire bridge were 

 exhibited by Mr. F. W. Burstall. The resistance box was of 

 the dial pattern, wound in bare platinum silver wire on strips 

 of mica, the wire being immersed in pure mineral oil ; there 

 were five dials, ranging from tV ohm to 1000 ohms, and four 

 pairs of proportional arms. The four standard coils were of 

 similar forms, but were intended to be used with mercury cups. 

 In conjunction with Mr. H. R. J. Burstall, the same exhibitor 

 showed bare wire resistance thermometers for use in vessels 

 under high jiressure. The measuring wire was wound on mica 

 plates carried by slender columns from a metallic plug which 

 was screwed into the vessel. The change of resistance was 

 measured by comparing the drop of E.\f.F. over the measuring 

 ■wire, with the drop over a standard coil put in series with 

 it and a battery. .\ thermometer was exhibited which had been 

 .in a steam .superhe.iler for more than a week conlinuuusly, at a 



NO. 1385, VOL. 54] 



pressure of 160 lb. per square inch. Both the.se exhibits 

 should prove of great assistance in electrical and thermometric 

 measurements. 



New apparatus for measuring the magnetic permeability of 

 iron or steel was shown by Prof Ewing, F.R.S. The apparatus 

 allows measurements of permeability to be made with samples in 

 the form of short rods, and greatly simplifies the process. It 

 acts by making a magnetic comparison between the rod to be 

 tested and a standard rod, the magnetic qualities of which have 

 been determined ^eforehand. The magnetic detector, which 

 shows when the two rods have the same induction, consists of a 

 compass needle placed in a gap in an iron bar joining the two 

 yokes. From its analogy to the Wheatstone Bridge, the author 

 proposes to call the instrument a Permeability Bridge. It forms 

 a companion instrument to the hysteresis tester exhibited last 

 year. 



A flint glass prism of nine inches aperture and 45° refracting 

 angle was exhibited by Mr. J. Norman Lockyer, C. B. , F.R.S. 

 The prism has been constructed by the Brothers Henry, of 

 the Paris Observatory, and will be used as an objective prism for 

 photographing the spectra of stars. Mr. Lockyer also showed 

 the following : — Photograph showing positions of coronal 

 .spectrum rings in the total eclipse of the sun, April 16, 1893. 

 The original negative was taken by Mr. Fowler, at Fundium, 

 West Africa, with the 6-inch prismatic camera near the middle 

 of totality, with an exposure of forty seconds. In addition to 

 the images of a number of prominences, there were portions of 

 rings representing the radiation spectrum of the corona. The 

 brightest of the rings corresponds to the well-known corona line 

 1474 K, but the others have not been previously photographed. 

 AH the rings are most intense in the brightest coronal regions, 

 near the sun's equator. — Photographic spectra of a Cygni, 7 

 Cygni, and .\rcturus. The photographs were taken at South 

 Kensington uith a 6-inch objective prism of 45°, and illustrated 

 the difference between stars of increasing and stars of decreasing 

 temperature. Arcturus is a cooling star, almost identical with 

 the sun, while o Cygni differs very widely from the sun and is 

 getting hotter. The spectrum of 7 Cygni, like that of Arcturus, 

 consists of a very large number of lines, but as many of the 

 more prominent lines agree with those of a Cygni, and are 

 absent from the solar spectrum, this star must be classed with 

 those of increasing temperature. — Photographs showing the 

 spectra of helium and gas X in relation to the spectra of Orion 

 stars. The lines of the two gases were arranged in the series 

 deduced by Messrs. Runge and Paschen, and their distributions in 

 the spectra of Bellatrix, Rigel, 5 Orionis, ami Spicawere shosvn. 

 — Photograpliic map of the spectra of metals of the iron group. 

 The map extended from wave-length 3900 to 5900, and in- 

 cluded the spectra of iron, manganese, cobalt, nickel, chromium, 

 and uranium, as shown at the temperature of the electric arc. 

 Rowland's map of the solar spectrum formed the term of com- 

 parison, so that the wave-lengths of the lines could be read oft 

 directly from the map. 



Mr. F. .McClean, F.R.S., exhibited photographs of the 

 spectra of twenty-three characteristic helium stars. These stars 

 correspond l.> Class I.n of Lockyer (Phil. Trans., December, 

 1S92), who further attributed their spectrum to helium (/Vft. 

 Roy. Soc, May 9, 1S95). The hydrogen and helium were 

 indicated below the scale of wave-lengths. The enlargement 

 was Si times the original negatives. Mr. McClean also showed 

 photographs uf the spectra of six stars of the third magnitude, 

 illustrating I he transitions from type to type. 



Another s|)ectroscopic exhibit was by Prof Hartley, F.R.S., 

 whose subject was, however, terrestrial. He showed a series 

 of photographed spectra illustrating an investigation of the 

 Bessemer flame, as seen at the North Eastern Steel Co.'s 

 Works, at Middlesbrough-on-Tees, in which the presence of the 

 rare elemenl gallium was recognised by a single line in its 

 spectrum, and separated from both the metal and the ore of the 

 district. 



A remarkable exhibit, by Mr. Joseph Goold, consisted of steel 

 tuning-bars and synchroni.sing sound-generators. The new 

 synchronising sound-generator was a vibrating rubber having the 

 pitch or vibr.ition-period of the note to be elicited. The separate 

 partial-tones were thus developed singly with remarkable ])0\\ cr 

 and sweetness. These appliances have already led to iIk- 

 further discovery of vihralion-axes and -vortices, examples of 

 which were exhibited. 



Tire rapid photographic printing machines, exhibited by Mr. 



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