June 21, 1894J 



NATURE 



183 



a coil and suspended needle-mirror, forming a galvanometer, and 



a ball contact or ' coherer," or else a tube offiling-i, in circuit 



with the other two. Electric surgings in the air, or in a scrap 



.f wire pegged into the lid, increased the conductance of the 



circuit. A light tap on the cylinder reduced it again. A handy 



lan;p and scale enabled the deflexion of the needle to be seen. 



The surgings could be excited by giving sparks to an insulated 



sphere not far off, especially if the knobs supplying the sparks 



are well polished. 



~ The exhibit of Dr. E. C. Stirling, C.M.G,, F.R.S., was a 



eries of fourteen photographs, with two mapsani a geological 



iCtion illustrating the researches carried on at Lake Callabonna, 



1 South Australia, for remains of Diprotodon and other ex- 



:nct animals, in 1S93. A description of the work to which 



ihese phitographs reler is given in another part of this number. 



Gold leaf made by electro-deposition was exhibited by Mr. 



J. \V. Swan, F.R.S. This exhibit illuslra'.ed an attempt to 



produce gold leaf by electro-chemical instead of mechanical 



means. The leaves were prepared by depositing a thin film of 



gold on a highly polished and extremely thin electro copper 



deposit. The copper was then dissolved by perchloride of iron, 



leaving the gold in a very attenuated condition. The leaves 



were approximately four millionths of an inch thick, and some 



of them mounted on glass showed the transparency of gold very 



perfectly when a lighted lamp was looked at through them. 



Miss Edna Walter and Mr. H. B. Bourne had on view a 

 projective goniometer. By means of this instrument, devised 

 and constructed by the exhibitors, the projection of a crystal on 

 a sphere is actually accomplished, realising in practice the 

 fundamental assumption of the theory of crystallography ; the 

 instrument is thus of value in demonstrating the axioms of the 

 ■science. If necessary, angular measurements could be made from 

 the image, but these only attain an accuracy of about 40' in 60' 

 = one per cent., which is inferior 10 that attained wiihagonio- 

 oieter. 



Lord Kelvin showed a model illustrating the molecular tactics 

 of a q'lartz crystal. The crystalline molecule was represented 

 by a regular hexagonal prism of wood, the long diagonal of 

 the hexagon being 95 of the length of the prism. This gave 

 in the assemblage representing a quartz crystal of regular form, 

 the correct an>;le (3S' 13'; between the faces of the prism and 

 the faces of the terminal six sided pyramid. Each crystalline 

 molecule was marked on alternate sides wiih slips of blue and 

 red paper, to show the orientalional dil'ference between the 

 !'ernate sides of the piism and the absolute difTerence between 

 le alternate faces of the pyramid. The coloured slips were 

 placed obliquely to give the chiral quality of the crystalline 

 molecule and of the assemblage. Right-handed and left- 

 Imnded molecules were shown. All the piczj-electric and pyro- 

 icctric properties of the crystal (including the chiral piezo- 

 L-ctric pro,.erty discovered by Voigt) would be actually pro- ' 

 duced in the model, if copper and zinc were substituted for the 

 red and blue paper, and the individual prisms separated by j 

 elastic insulating material. The model showed the well-known 

 orientalional macling on two faces of the prisms, and the con- 

 tiguous pair of faces of the terminal pyramid. 



Dr. Isaac Roberts, F. K.S., showed original negatives and 

 •enlarged photographs of the spiral nebukv NIessier 74 Piscium, 

 Messier 101 Urspj Majoris, Messier 65 and 66 Leonis, Ilerschel 

 I. 16S Ur;a; Majoris, Herschel I. 56 and 57 Leonis. These 

 photographs revealed the forms and structures of the spiral 

 nebula,' with much grea'er detail and accuracy than had pre- 

 viously been known. They also clearly showed that the spirals 

 were almost perfect geometrical figures, but broken up into 

 numerous stars, or star-like condensations of the nebulosity, or i 

 of the meteoric matter, of which they are probably composed, 

 and thus furnish strong evidence of the truth of the nebular or 1 

 of the meteoric hypotheses. I 



A number of specimens illustrating locomotion phases in 

 decapod ciuslacea were exhibited by Prof. Siewait, who also 

 •showed mummy cloth, of not later thin 4CO0 B.C., compared 

 with finest Irish linen of to-day. The piece of mummy cloth, • 

 made not later than 6000 years ago (IVth Egyptian Dynasty), 

 *as shown by the side of a piece of linest Irish linen 140 ■ 140 

 of to-day. The strands of the mummy cloth were 300 150 

 per inch. 



Specimens of metallic chromium, manganese, tungsten iron, 

 Ac, free fiom carbon, also fused alumina, obtained during re- 

 duction of the metallic samples, were exhi'iited by Mr. Claude 

 Vaulin. The specimens of metallic chromium, manganese, &c. , 

 had been reduced from their oxides by means of metallic alun- 



inium. The oxide of the metal to be reduced was intimately 

 mixed with finely divided aluminium, and heated in magnesia- 

 lined crucibles. The heat produced by the oxidation of alum- 

 inium during the operation was sufhcient to fuse alumina, 

 specimen of which was exhibited. 



Prof. A. M. Worthinglon, F.R.S., and Mr. R. S. Cole ex- 

 hibited photographs of a splashing drop. The photographs 

 shown were obtained by allowing a drop to fall in absolute 

 darkness, and illuminating it at any desired stage of its 

 splash by a suitably timed Leyden jar discharge taking place 

 between magnesium terminals. The exhibit comprised (i) 

 shadow photographs obtained when a drop of mercury 

 fell on the sensitive plate itself, which was laid horizontally 

 and illuminated from above ; (2) objective photographs, 

 showing much more detail than has usually been obtained in 

 such instantaneous work, and illustrating the exquisite sen-itive- 

 ness of the very rapid modern plates. To obtain these photo- 

 graphs the spaik was produced at the focus of a deep, silvered 

 watch glass subtending an angle of nearly 180', and was brought 

 very near to the place of impact. .\ single quartz spectacle 

 lens was substituted for the usual lens of the camera, and thus 

 the absorption of photographic rays by glass was avoided. 



Mr. \V. Kurtz {.Vew Vork) exhibtted photographic prints in 

 the natural colours, obtained by printing in the three primary 

 colours only 1 Dr. Vogel's process';. The prints shown were all 

 of them printed in thrie colours only, some by surface-prin:ing, 

 the others by lithography ; but in all cases the printing blocks 

 were produced by photography. The process employed is as 

 follows r — By the intervention of suitable media, three photo- 

 graphs are obtained, severally appropriate to the three primary 

 colours composing the original picture or view re'iiired to be 

 reproduced. From these three photographs, respectively due to 

 the chemical action of th; red, yellow, and blue rays of the 

 spectrum, printing blocks are prepared, which bein' printed 

 from in red, yellow, and blue ink, give the multi-coloured 

 effects shown by the specimens. 



Prof. Elisha G ay exhibited the telautogiaph, an instrument 

 for transmitting intelligence by electricity. Tne writer at one 

 station u^ing a lead-pencil, attached mechinic.ally to the ap- 

 paratus, and writing upon ordinary paper, transmits to the 

 distant station a facsimile of his handwriting, at his ordinary 

 writing speed. Sketches, sketch-portraits, diagrams, plans, 

 trademarks, and the like, as well as the characters of hiero- 

 glyphic alphabets may also be transmitted. 



The following exhibits, with demonstratlo.is by means of 

 the electric lantern, took place in the m;e'.ing room of the 

 Society : — 



The magic mirror, by Mr. J. W. Kearton. It was shown 

 that the English magic mirror owes its peculiar properties to 

 curved elevations and depressions in the polished metallic f.ice, 

 the elevations producing figures in shade by scattering of light, 

 and the depressions, figures in light by condensing rays reflected 

 from the mirror on to a screen. The figures in relief and in- 

 taglio are first produced by the action of any suitable acid on 

 the metal plate, and are then polished down until thev disappear 

 to direct vision. The figures of the Japanese type of mirror are 

 by-products in the process of minuficlure, and arise from local 

 yieldings of the f.ice and back during polishing : the more rigid 

 parts of the face, which correspond 10 raised metallic figures on 

 the back, suffer a somewhat greater reduction from opposing 

 greater resistance to the polishing tool. 



As at the previous conversazione. Prof. E. B. Poulton gave 

 illustrations of recent work upon the influence of environmet.t 

 upon the colours of certain lepidopterous larvx. 



Mr. D. Morris, C. M.G., exhibited and described a series of 

 views illustrating the leading features of tropical vegetation. 



A CHEMICAL METHOD OF ISOLATIXG 

 FLUORIXE. 



\ NEW salt of exceptional interest, the first member of 

 ^^ a series of flacrplumbates, is described by Dr. Brauner, of 

 Prague, in the June issue of the Jouina! of the Chem cal 

 Society. Dr. Branner is well known in this country, having 

 been Berkeley Fellow of the Owens College, Manchester, 

 previous to his appointment to the chair of chemistry in the 

 Bohemian University. Twelve years ago he described two 

 compounds very rich in fluorine, CeF, . H._,0 and 3''^'' • zCeFj. 

 2H.jO, and .showed that when heated they first gave up their 

 water and subsequently evolved a gas which possessed an odour 

 similar to that of hypochlorojs acid, and which exhibited the 



NO. 1286, VOL. 50] 



