578 



NATURE 



[October 9, 1890 



we do not get the advantage of the whole conductivity of the 

 metal for alternate currents. When the conductor is too thick, 

 we have in part of it comparatively ineffective copper present ; 

 but, so far as is known, it has generally been supposed that the 

 thicker the conductor the greater will be its whole effective 

 conductance, and that thickening it too much can never do 

 worse than add comparatively ineffective copper to that which is 

 most effective in conveying the current. It might, however, be 

 expected that we could get a positive augmentation of the 

 effective ohmic resistance, because we know that the presence of 

 copper in the neighbourhood of a circuit carrying alternating 

 currents causes a virtual increase of the apparent ohmic resist- 

 ance of the circuit in virtue of the heat generated by the currents 

 induced in it. May it not be that anti-effective influence such as 

 is thus produced by copper not forming part of the circuit can 

 he produced by copper actually in the circuit, if too thick? 

 Examining the question mathematically. Sir William finds that 

 it must be answered in the affirmative, and that great augmenta- 

 tion of the effective ohmic resistance is actually produced if the 

 conductor is too thick, especially in coils consisting of several 

 layers of wire laid one over another in series around a cylindric 

 or flat core, as in various forms of transformer. 



Prof. J. A. Ewing, in a most interesting and important com- 

 munication {vide Phil. Mag., September 1890), exhibited a 

 model to illustrate some novel ideas on the molecular theory of 

 induced magnetism. The present notion of a quasi- frictional 

 resistance opposing the turning of the molecular magnets lends 

 itself well to account for the most obvious effects of magnetic 

 hysteresis and the reduction of hysteresis by vibration. On the 

 other hand, it conflicts with the fact that even the feeblest mag- 

 netic force induces some magnetism. Reference was made to 

 another (and not at all arbitrary) condition of constraint, which 

 not only suffices to explain all the phenomena of hysteresis, 

 without any notion of friction, but seems to have in it abundant 

 ■<;apability to account for every complexity of magnetic quality. 

 Prof. Ewing supposes that each molecular magnet is perfectly 

 free to turn except in so far as it is influenced by the mutual 

 .iction of the entire system of molecular magnets. A model 

 molecular structure was exhibited, consisting of a large number 

 of short steel bar-magnets strongly magnetized, each pivoted 

 upon a sharp vertical centre, and balanced to swing horizontally. 

 The bars swing with but little friction, and their pole-strengths 

 are sufficient to make the mutual forces quite mask the eirth's 

 -directive force when they are set moderately near one another. 

 The group is arranged on a board which slips into a large frame 

 wound round the top, bottom, and two sides, with a coil, through 

 which an adjustable current may be passed to expose the group 

 to a nearly homogeneous external magnetic force. 



Sir William Thomson read a paper on a method of determin- 

 ing in absolute measure the magnetic susceptibility of diamagnetic 

 and feebly magnetic solids. The method proposed consisted in 

 measuring the mechanical force experienced by a properly shaped 

 portion of the substance investigated, placed with different parts 

 of it in portions of magnetic field between which there was a 

 large difference of the magnetic force. A cylindrical or rect- 

 angular or prismatic shape terminated by planes perpendicular 

 to its length was the form chosen ; the component magnetic 

 force in the direction of its length was equal to i/x(R- - R'^)A ; 

 where ix. denotes the magnetic susceptibility, R R' the magnetic 

 force in the portions of the field occupied by its two ends, and 

 A the area of its cross-section. 



Lord Rayleigh read a paper on the tension of water surfaces, 

 clear and contaminated, investigated by the method of ripples. 

 The ripples were rendered visible by a combination of Foucault's 

 optical arrangement with intermittent illumination. Two fre- 

 quencies were used, about 43 and 128 per second. The surface- 

 tension of a clean water surface, in c g.s. measure, was found 

 to be 74 '°» thus confirming observations made with capillary 

 tubes. Water saturated with olive oil had a surface-tension 

 of 41 "o, and saturated with oleate of soda a surface-tension 

 of 25-0. 



Mr. W. N. Shaw reported on the state of our knowledge of 

 electrolysis and electro-chemistry. 



Mr. J. Hopkinson read a paper on the inland compared with 

 the maritime climate of England and Wales. For special reasons 

 Buxton, Woburn (Apsley Guise), Croydon, Cheltenham, and 

 ■Churchstoke were chosen to represent the interior of the 

 -country, while Scarborough, Lowestoft, Babbacombe, Worthing, 

 and Llandudno were chosen to represent the sea-coast. The 

 places were so chosen that the mean position, latitude, and 



longitude of the five inland places should closely approximate l. . 

 those of the maritime. As the result of observations extending 

 over the decade from 1880-89, he concluded that, so far as regards 

 our comfort and most probably also our health, our maritime 

 climate is on the whole superior to our inland climate, being 

 warmer, owing (it is most important to observe) to the nights not 

 being so cold, while the days are no hotter, the extremes of tem- 

 perature being much less, the air rather less humid, the sky less 

 cloudy, and the rainfall less. 



Prof. Ramsay read a paper on the adiabatic curves for ether, 

 gas and liquid, at high temperatures. The method adopted in 

 the experiments was an ingenious one, and consisted in deter- 

 mining the velocity of sound in the vapour by Kundt's dust- 

 figures, from observation of the wave-length and the pitch of the 

 note emitted by the stroked tube containing the vapour. This 

 process gives the ratio of adiabatic and isothermal elasticity 

 from which the former elasticity can be calculated as the latter 

 is known. 



Prof Ostwald read an interesting paper on the action of 

 semi-permeable membranes in electrolysis, in which he gave an 

 account of experiments upon the passage of an electric current 

 through solutions in series separated by semi-permeable mem- 

 branes, and pointed out the importance of such phenomena to 

 physiology. He explained that a semi-permeable membrane 

 would allow ions of one kind to pass through, but arrest ions of 

 another kind, and thus act as though it were a metallic electrode. 



Prof. C. Piazzi Smyth sent a paper on photographs of the in- 

 visible in solar spectroscopy. Two photographs were shown, 

 each measuring 40 inches long x 20 inches high. They represent 

 in reality, only very small portions of the faint ultra-violet of the 

 solar spectrum, but on a whole scale of 57 feet long from red to 

 violet ; and are located quite outside the spectral limit of vari- 

 ability to the human eye, with the grating spectroscope con- 

 cerned, whether under summer or winter sun. 



Profs. Riicker and Thorpe contributed a paper on regional 

 magnetic disturbances in the United Kingdom, and this was 

 followed by a paper upon similar disturbances in France, by 

 Prof. Mascart. A point of great interest in connection with 

 these papers was the continuous nature of the disturbances ex- 

 tending from the one country across the Channel to the other. 



Prof. Lodge, in a paper on electrostatic forces between con- 

 ductors, gave an account of an investigation into the forces 

 between electric resonators as examined experimentally by Boys, 

 and therefrom branched out into several allied subjects connected 

 with the mechanical forces of electric pulses and waves. 



Prof. Fitzgerald communicated several papers on mathematical 

 physics to the Section. One of these bore what would have 

 been an attractive title, "An Episode in the Life of J," had it 

 not been for a parenthetical addition, viz. " (Hertz's Solution of 

 Maxwell's Equations)." It may be remarked that J has nothing 

 to do with Joule or his equivalent, and that the episode referred 

 to was not of the popular anecdotal type. 



Mr. W. Barlow, in a paper on atom-grouping in crystals, called 

 attention to some very interesting properties of the simpler kind 

 of symmetrical grouping of points, and pointed out an easy and 

 effectual method of studying them by using a model consisting 

 of equidistant parallel planes of homogeneously distributed 

 points represented by beads. 



Mr. W. H. Preece read a paper on the character of 

 steel used for permanent magnets. Samples of steel for the 

 experiments were obtained from all the leading firms, and after 

 magnetization were tested by a magnetometric method. The 

 marked superiority of the Marchal magnets over those made of 

 English steel is due either to the quality of the steel, or to the 

 mode of tempering — most probably the latter. 



Prof. S. P. Thompson read a paper on the use of fluor spar 

 in optical instruments, in which he referred to the existing uses 

 of fluor spar for experiments on radiant heat, and in the " apo- 

 chromatic " microscope lenses of Zeiss. The latter application 

 derives its importance from the extremely low dispersion rela- 

 tively to the mean refractive power of the material. To these 

 applications the author now added that o£«the construction of 

 spectroscopic direct-vision prisms ; and he described two prisms, 

 both constructed for him by Mr. C. D, Ahrens— one consisting 

 of a fluor prism cemented between two flint-glass prisms, and 

 the second consisting of one Iceland-spar prism cemented be- 

 tween two fluor prisms. The former was considerably shorter 

 than the ordinary direct-vision prism of equal power : the latter 

 had the property of polarizing the light as well as dispersing it, 

 and presented the novel feature of a true polarispectroscope. 



NO. 



:o93, VOL. 42] 



