June 20, 1895] 



NATURE 



181 



illustrated. Both tuning-forks and a mechanical device were 

 eiuiiliiycd to produce the ripples. By the use of "scale lines," 

 the logarithmic chart was made more comprehensive than usual. 

 The lines were employed to illustrate the effect of all possible 

 variations of gravity and of surface tension divided by density 

 upon velocities and frequencies of waves and ripples. 



Mr. J. Norman Lockyer, C. B. , had three exhibits. One was a 

 photograph of apparatus employed for collecting the gases obtained 

 from minerals by the distillation method. A small retort con- 

 taining the mineral is connected with an end-on spectrum tube 

 joined on to a Sprengel pump. -After exhaustion, the mineral is 

 heated to redness, and the spectra of the gases evolved at the 

 various stages, as exhibited by the spectrum tube, are both 

 observed and photographed. The gases are collected in a 

 "steeple" at the foot of the fall tube of the pump, and 

 they can then be observed at atmospheric pressure. The 

 second exhibit consisted of photographs of the spectra of 

 Bellatrix, and of a part of the solar chromosphere, showing co- 

 incidences with the lines photographed in the spectra of the 

 gases obtained from uraninite. The photographs showed a 

 ■close relation of the new gas or gases to solar and stellar 

 phenomena. They appear to point to the vera airisa, not of two 

 or three, but of many of the lines which so far have been 

 •classed as " unknown." The spectrum of Bellatrix was jjhoto- 

 graphed at South Kensington with a 6-inch prism of 4^", and that 

 of the solar chromosphere with the same instrument during the 

 total eclipse of the sun, 1893. Mr. Lockyer also ex- 

 hibited photographs of the spectra of the new gases. In 

 the preliminary experiments, the new gases have not been 

 separated from the known gases which come over with 

 them, so that the spectra exhibited contained many known lines. 

 The photographs illustrated : (a) The 'presence of the yellow 

 line (U3) in some instances wi't/i the blue line 4471, and in 

 others without it. {b) The presence of the yellow^ line in some 

 spectra with an ultra-violet line at 3889, and in others without it. 

 Dr. A. A. Common exhibited the following silvered glass 

 mirrors: (l) 21-inch convex mirror, 54-inch radius, being the 

 small mirror of an oblique Cassegrain reflecting telescope. 

 ^2) 20-inch concave mirror, 90-inch radius, spherical curve. 

 {},) Two 16-inch plane mirrors for heliostats to be used at the 

 1896 total solar eclipse. 



Air. .\. E. Tutton exhibited an instrument for cutting, grind- 

 ing, and polishing accurately orientated plates and prisms of 

 •crystals of every degree of hardness. The instrument combines 

 an accurate reflecting goniometer \\ ith a diamond-edged cutting 

 •disc and grinding and polishing laps. The adjusting segments 

 of the goniometer are graduated, in order that the crystal may 

 be adjusteil so that the desired direction in it can imme^liately 

 be brought i>arallel to the cutting disc or grinding lap. Numerous 

 interchangeable l»ps are provided suitable for all classes of 

 crystals, and the interchange may be effected with great readi- 

 ness. A counterpoising arrangement is also provided which 

 ■enables the pressure with which the crystal bears upon the lap 

 to be nicely adjusted, according to the strength of the crystal. 

 The instrument may either be driven by hand or by means of 

 any form of small motor. 



Mr. A. P. Trotter showed a model illustrating the relation of 

 volts, amperes, and length of electric arc. The model was made 

 from the diagrams in Prof. Ayrlon's paper, read before the 

 Chicago Congress, and described in Mrs. ,\vrton"s article in The 

 Elcctridau. Drawings of the electric arc were shown by Mrs. 

 Ayrton. The drawings were in sepia, and ten times the full size. 

 They showed the form of the arc produced with a current of 20 

 am^>eres between a positive carbon 18 millimetres in diameter, 

 and a negative one 15 millimetres in diameter, when the 

 uc was respectively 4, 7 and 18 millimetres long. Eroni 

 (lie drawings it could be seen that using a cored positive 

 carbon diminishes the visible jiart of the arc, and, when the arc 

 is long, causes the central portion to become gourd-shaped. 



The Applied Mathematics Department of University College 

 •showed a series of diagrams, calculated and prepared by Miss 

 Alice Lee, to illustrate the time-decay of the tield due to a 

 Hertzian oscillator. The late I'rof. Hertz prepared four 

 diagrams to illustrate the nature of the field in the neighbour- 

 hood of an oscillator giving a stable wave train. His theory 

 requires modification, owing to every Hertzian oscillator really 

 giving a rapidly damped wave train. Miss Lee's diagrams illus- 

 trated the changes in the field during 6^ complete oscillations. 

 Four systems of curves gave the points of the field with relative 

 strengths 50, 30,10 and i. The decadence of the field was repre- 



NO. 1338, VOL. 52] 



sented not only by the gradual change of shape of the curves, 

 but by the complete disappearance of the cur\'es of greater 

 strength. When the series is complete, it is proposed to reduce 

 it by photography and use it in a " wheel of life," to illustrate 

 the decadence of an oscillator-field. 



A curious model for showing the gyroscopic properties oi a 

 wheel was exhibited by Mr. Killingworth Hedges. The wheel 

 was represented by a rim, having within it a heavy inner disc 

 which could be made to revolve rapidly on the axis of the 

 wheel. When the wheel was allowed to roll slowly down an 

 inclined plane, and the inner disc was made to revolve in the 

 same direction as the wheel, they both assisted to keep the 

 system upright. When, however, the inner disc revolved in 

 the opposite direction to the wheel, the system was in a state of 

 unstable equilibrium which caused a rapid revolution through 

 180°, when both the wheel and the inner disc revolved in the 

 same direction, and so produced a state of stable equilibrium. 



Four photographic views taken by Mr. W. Bartier, and illus- 

 trating the accumulation of ice on the river near the Beckton 

 Gas Works, North Woolwich, in February of this year, were 

 shown by Mr. G. J. Symons. 



Photographs of curvilinear crystals of water were exhibited by 

 Dr. Gladstone, F. R.S. The photographs were taken during 

 the severe frost of last February, and showed the forms assumed 

 by the vapour when frozen upon a shoji window, and the glass 

 roof of a photographer's studio. All the lines of the crystals 

 were curved. Another exhibit by Dr. Gladstone consisted of a 

 blue photograph showing the way in which a solution of sodium 

 salts mixed with some earthy matter and water may be made to 

 crystallise on evaporation. This specimen showed many spiral 

 forms. It, and the original specimens, were prepared by Mrs. M, 

 Watts Hughes. 



Prof. A. G. Greenhill and Mr. T. I. Dewar exhibited an 

 algebraical spherical catenary. By a special choice of the con- 

 stants, depending upon the quinquisection of the period of the 

 associated elliptic functions, the general equations of the 

 spherical catenary, considered by Clebsch in Crelle, 57 were 

 shown reduced so as to make the projection of the chain on a 

 horizontal plane a closed algebraical curve of the tenth degree. 



A number of interesting Japanese pictures, selected to illustrate 

 the effects of time on the pigments used by tlie old painters 

 of Japan {a.D. 1322 to the early part of the igth century), 

 were exhibited by Mr. W. Gowland. The chief pigments used 

 in these pictures were as follows : — Greens and blues : carbonates 

 of cojiper. Permanent blue : the mineral Lapis lazuli. Reds : 

 red oxitle of iron, vermilion, carmine. Permanent white : 

 levigated oyster-shells. Black : soot prepared from the oil of 

 Sesaiuttin Ifidiium^ 



Tropical American butterflies, selected to show the existence 

 of common colour-types among species associated in the same 

 areas, were exhibited by Mr. W. F. H. Blandford. The phe- 

 nomenon ( Homaoihromatism ) is observed chiefly among species 

 of the sub-families Daitaimc and Heliconiiiut, but frequently 

 species of other sub-families conform to the prevailing colour- 

 type. To a particular class of cases of colour-resemblance the 

 term "mimicry" has been applied. The .series shown com- 

 prised : — (l) Species oi Heliconius3s,soz\-!Ae.A in pairs, the colour- 

 type varying with the distribution from north to south. {2) 

 Species of diflerent genera ( Tithorea and Helieoiiius) associated 

 in pairs, and sometimes mimicked by butterflies of other 

 families. (3) Homceochromatic types from various districts 

 represented by numerous species in different families, sub-families 

 and genera. 



.\linutiiu in finger-prints formed the exhibit of Mr. Francis 

 Galton. The exhibit furnished an illustration of the exceptional 

 trustworthiness of the finger-print method in determining ques- 

 tions of identity. It demonstrated that in a case of twins, whose 

 portraits, classificatory measures, and finger-print formula: were 

 closely alike, the finger-]irint minutia; were quite different. .-V 

 second exhibit of Mr. Gabon's was the print of the hand of 

 a child eighty-six d,ays ol<l. \\\ enlargement of this print showed 

 the development of the ridges at that early age. 



.Mr. B. Harrison exhibited Eolithic implements from the 

 chalk plateau of Kent. The implements were found by the 

 exhibitor in pits, dug under the auspices of the British Associa- 

 tion. Stones were shown which were thought to bear evidence 

 of use as tools, naturally of suitable shapes, but improved upon 

 by chipjiing roimd the edges where required. 



The Curator of the Maidstone Museum showed a series of 

 nine photographs (with map, ground plan, and section) of a 



