May 19, 1898] 



NATURE 



61 



THE ROYAL SOCIETY'S CONVERSAZIONE. 



"THE first soiree this year was held on the nth inst. It was 

 numerously attended, and a large number of objects had 

 be;n brought together. We have not space to refer to all the 

 exiibits. 



^'rof. Hele-Shaw exhibited experiments on the flow of water. 

 W« have already given an account of some of these (p. 34). 

 Prof. Hele-Shaw also showed instruments for describing cyclo- 

 ida curves and envelopes. By means of the instrument ex- 

 hibted, two surfaces of cardboard or paper are made to revolve 

 so hat imaginary pitch circles on each roll upon one another. 

 This is effected by employing auxiliary circles within or with- 

 out the pitch circles, the auxiliary circles being made to move 

 at the same velocity by passing between two pairs of equal 

 wheels, each wheel being connected by an axle with the corre- 

 sponding wheel for the other auxiliary circle. By a further 

 combination of wheels the actual centres of rotation are dis- 

 pensed with, only virtual centres being used. Hence it is 

 possible to draw with a small instrument cycloidal or involute 

 curves for circles of any radius, however large, and to find 

 enveUpes or centrodes under any conditions of fixed or varying 

 radii. A simple practical application is that to the teeth of 

 wheel;, examples of which were exhibited. 



Mr. J. Mackenzie Davidson exhibited Rontgen ray apparatus 

 for localisation purposes. 



Mr. T. Andrews, F.R.S., exhibited (i) micrographic illus- 

 trations of deterioration in steel rails. These high power in- 

 vestigaions of old rails, which have worn well, afford an in- 

 ■dicatior of the microscopic structure and composition best 

 adapted to ensure endurance and safety in rail service. (2) 

 Micro-CTystalline structure of iron. The micrographs indicate 

 the existence of a primary and secondary crystalline formation 

 in large masses of iron which have been slowly cooled. 



Mr. C Orme Bastian showed an electric current meter act- 

 ing by electrolysis. The height of a column of liquid (sulphuric 

 acid and water) contained in a glass tube is caused to decrease 

 by electro-decomposition, and this decrease in height is utilised 

 to indicate the quantity of current (in ampere hours) that has 

 passed through the meter in any given time. Assuming the 

 voltage of the supply to be constant, a perfectly accurate 

 measure of the electric energy, which has passed through the 

 meter, is recorded by means of a scale in front of the above- 

 mentioned lube, which can be calibrated in Board of Trade 

 or other units. A hole in a rubber plug at the top of the tube 

 allows the gases resulting from the electro-decomposition of the 

 liquid to pass away into the atmosphere, through the gauze tray 

 and holes in the top of the meter case. Parafifin on the surface 

 of the fluid prevents atmospheric evaporation. The instrument 

 starts registering with an infinitely small current ; it is accurate 

 at all temperatures and at all loads ; its accuracy is unaffected 

 by temporary excess currents ; and it is not capable of being 

 affected by outside disturbing influences. 



Dr. Leonard Hill and Mr. Harold Barnard showed simple 

 forms of sphygmo-manometers. 



Admiral Sir W. J. L. Wharton, K.C.B., F.R.S., and Prof. 

 J. W. Judd, C.B., F.R.S., exhibited, on behalf of the Coral- 

 Reef Committee of the Royal Society, charts, sections and 

 specimens, illustrating some of the results of the investigations 

 carried on in the atoll of Funafuti (Ellice Group), South Pacific. 

 Prof. Poulton, F R.S., showed insects captured in Canada 

 and some adjacent States during a visit in connection with the 

 meeting of the British Association in 1897. The insects in this 

 collection are not of any special interest on account of rarity, 

 |)ut they serve to convey an impression of the general character- 

 istics of this section of the fauna by which the traveller is 

 surrounded as he proceeds, at the time of the year indicated in 

 the labels, across the American Continent on a line not far 

 <listant from the Canadian southern boundary. The general 

 similarity of the Lepidoptera to those of Europe is remarkable. 

 Attention is directed to the geographical data on the small 

 fjrinted labels. The cases are arranged so that the left hand 

 represents the westernmost locality (Vancouver Island), the 

 right hand the easternmost (Quebec). 



Dr. H. Gadow, F.R.S., and Mr. W. F. Blandford exhibited 

 I series of models, illustrating the composition of vertebra; in 

 !'.e Various groups of vertebrata. 



Prof. T. Rupert Jones, F.R.S., and Mr. J. Ballot showed a 

 '-Ties of large stone implements, collected by Sidney Ryan, 



Esq., from the tin-bearing gravels of the River Embabaan, in 

 Swaziland, South Africa. 



Mr. Alan A. Campbell Swinton exhibited (i) experiments 

 upon the circulation of the residual gaseous matter in Crookes* 

 tubes. Radiometer mill wheels are employed to detect the 

 direction and velocity of the gaseous streams, and the experi- 

 ments indicate that in very highly exhausted tubes of the locus 

 type, in addition to the well-known negative stream from the 

 kathode, discovered by Crookes, there exists also a positively 

 electrified stream from the anode, which travels in the opposite 

 direction to the kathode stream, and is exterior to the latter. 

 Mill wheels of various forms and of both non-conducting and 

 conducting material show these effects. (2) Rontgen ray camera, 

 showing the position, dimensions and form of the source of the 

 X-rays in a Crookes' tube. (3) Kathode ray lamps. The 

 kathode rays from two concave kathodes placed opposite to one 

 another and supplied with an alternating electric current of 

 about 20,cxx) volts pressure, are focussed upon a button of 

 refractory material, which is thus raised to a very high tempera- 

 ture and becomes brilliantly incandescent. The efficiency in 

 terms of the amount of light produced for a given quantity of 

 energy siipplied to the lamp, appears to be much superior to 

 that obtained in ordinary incandescent electric lamps, and under 

 suitable conditions may even exceed that of the arc. 



Mr. J. Wimshurst showed improved apparatus for holding, 

 and for the excitement of Rontgen ray tubes ; Mr. Killingworth 

 Hedges, specimens of copper rapidly deposited at high current 

 densities ; and Prof. J. P. O'Reilly, a set of fourteen original 

 coloured drawings of the principal cromlechs existing in the 

 vicinity of Dublin. The drawings being plans and sections to 

 scale, tend to show that the cromlechs in question were oriented 

 truly : (a) either as regards their side walls (Druid's (ilen) 

 (Shankell), or {b) present in their arrangement indications, 

 which point to bearings either N. by S. and E. by W., or to 

 the points of the summer and winter solstices ; or, as the case 

 of the Glen Druid Cromlech, an inclination of the cap stone 

 marking the altitude of the winter sun at the solstice (14° 

 approx.), and consequently tending to prove that the cromlechs 

 were designed, amongst other uses, to allow of astronomical 

 observations being made with a view to the determination of 

 fixed periods of the year or commencements of seasons. 



The Rev. Walter Sidgreaves, S.J., showed the spectrum of 

 Mira (o Ceti) compared with the spectra of other stars of 

 Secchi's third type ; and Mr. K. J. Tarrant, photographs of 

 electrical discharges. 



Mr. W. Ellis, F.R.S., showed smoothed curves of sun-.spot 

 frequency (Wolf), compared with corresponding curves showing 

 the variation in diurnal range of the magnetic elements of de- 

 clination and horizontal force from ob.servations made at the 

 Royal Observatory, Greenwich. A graphical representation of 

 the periodical variation in frequency of sun-spots, and of the 

 amplitude of the diurnal magnetic movement. The average 

 length of the period is about eleven years, subject, however, to 

 a variation of one or two years or more, which the sun-spot 

 and the magnetic curves alike exhibit. There is also a corre- 

 sponding variation in intensity at the different epochs of maximum 

 effect. 



Mr. R. B. Roxby had on view specimens of " Naturographs " 

 (prints produced by Dr. Selle's process of photography in natural 

 colours). 



Mr. C. V. Boys, F.R.S. , showed phase reversal and silver 

 zone plates made by Mr. R. W. Wood, of the University of 

 Wisconsin. These plates are made with 230 zones. In con- 

 sequence of the great number, their equivalence to a lens in 

 image-making is very complete. Some are printed on bichro- 

 mated gelatine. These are stated to be " phase reversal," i e. 

 the thickness is such that alternate zones are in opposite phases, 

 so the whole surface is operative. Two of these, of about 70 

 and 13 cms. focus, are mounted as a telescojje, and show a 

 magnified image of incandescent electric lamps. Others are 

 photographed upon metallic silver by coating a deposited film 

 on glass with bichromated gelatine, exposing, washing, exposing 

 to iodine, dissolving with " hypo," and finally washing off the 

 remaining gelatine when the lines acted upon by light are left as 

 bright silver, the rest being tjansparent glass. One is elliptical, 

 with axes in the ratio of sJ 2 : i. If this is placed on thehypo- 

 thenuse of a right-angled prism with Canada balsam, it will give 

 images due to the difference of phase between the light totally 

 reftected and that metallically reflected on alternate zones. 



NO. 1490, VOL. 58] 



