282 



NATURE 



\yuly 17, 1879 



To Sir William Thomson my thanks are due for the im- 

 proved parallel slide and other details, and also to Mr. Lege 

 (the maker of the instrument) for the design of the wheel- 

 gearing. 



" The Motion of Two Spheres in a Fluid." By W. M. Hicks, 

 M.A., St. John's College, Cambridge. Communicated by Prof. 

 J. Clerk Maxwell, F.R.S., Professor of Experimental Physics in 

 the University of Cambridge. 



The investigation is based on the lemma that the image of a 

 source in an infinite fluid in presence of a sphere consists of a 

 source at the inverse point of the former, and a line sink thence 

 to the centre of the sphere. From this is deduced the image of 

 a doublet whose axis passes through the centre of the sphere, 

 and of one whose axis is perpendicular to this. Thence is found 

 the kinetic energy of motion of two spheres and fluid in which 

 they are immersed, and properties of the motion deduced by 

 Lagrange's equations. Amongst other things is considered the 

 action between vibrating spheres. 



Physical Society, June 28.— Prof. W. G. Adams in the chair. 

 New Members : Mr. J. F. Moulton, Mr. J. J. Eastwick.— Prof. 

 W. G. Adams exhibited his new measuring polariscope. It 

 consists of three principal parts. The lower section consists of 

 a mirror, a lens, a Nicol's prism, and two other lenses. The 

 upper section consists of lenses and Nicol's prisms arranged 

 in the reverse order. Each lens and Nicol's prism is supported 

 separately by screws, and its position can be altered indepen- 

 dently of the others. These two parts form a complete polari- 

 scope. Besides these there is a middle piece consisting of two 

 lenses (nearly hemispheres) forming a box to inclose the crystal 

 immersed in oils, their curved surfaces being concentric. The 

 whole middle piece is supported on the tubes of the upper and 

 lower portions, and may be turned about the optical axis of the 

 instrument. The vertical graduated circle carrying the central 

 lenses and crystal may be turned through any angle about its hori- 

 zontal axis. By means of an arc fastened perpendicularly on the 

 graduated circle with the centre at the centre of curvature of the 

 central lenses, the crystal may be turned about another horizontal 

 axis at right angles to the former, so that the crystal and the cen- 

 tral lenses can be turned about each of three axes which are mutu- 

 ally at right angles. By means of a system of toothed wheels in 

 gear with the rims of the central lenses, the crystal and central 

 lenses may be turned separately about the optic axes of the 

 instrument, so as to bring the planes of the optic axes of a 

 biaxial crystal parallel to the plane of the vertical graduated 

 circle. — Sir John Conroy, Bart., read a paper on the distribu- 

 tion of heat in the spectrum. After referring to Dr. J. W. 

 Draper's supposition that all the rays in the spectrum have the 

 same heating effect, and to his statement that owing to the 

 unequal dispersion of the prism for rays of different refrangi- 

 bility, the method that has been usual for determining the 

 calorific intensity of the various parts of the spectrum is an 

 essentially defective one ; the author described a graphical 

 method for eliminating the effect of the unequal dispersion of 

 the prisms, and showed that from MM. Fizeau and Foucault's 

 measurements, and also from those of Lamansky and Prof. 

 Tyndall, that the maximum intensity is about the middle of the 

 visible spectrum, and not at the red end ; and, further, that the 

 curves given by various observers as representing the intensity 

 of the heat in different portions of the spectrum, are in reality 

 the " dispersion curves " for the particular prisms employed. — 

 Capt. Abney, R.E., called attention to his published paper on 

 the measurement of the so-called thermo-spectrnm, wherein he 

 shows that the distribution of heat in the spectrum is a mis- 

 nomer, and that what was really measured by Lemansky and 

 Tyndall was the energy absorbed by the lamp-black and 

 the absorption due to the prisms used. He considered that 

 there was no inherent heat in the spectrum. He found 

 that Dr. Draper had not taken into account the amplitude. 

 Prof. Guthrie said that Capt. Abney had expressed what 

 many thought, namely, that heat was radiant energy. — Mr. 

 Grant then described an investigation which he had made 

 into the induction lines round two parallel coils of wire. In the 

 primary coil an intermittent current of electricity from a Le- 

 clanche battery flowed ; and in the secondary a telephone was 

 connected up to detect the induction sounds. With this apparatus 

 he found that with the coils kept parallel to each other, there 

 were lines, or rather a surface of minimum induction surrounding 

 the primary, and that if the secondary were placed in these lines 



hardly any induction noise could be detected. A diagram repre- 

 senting a medial section through the coils showed the lines to 

 proceed from the wire of the coils in two curves resembling 

 parabolas — one from each cross-section of the wire outwards. — 

 Dr. Shettle then described his experiments proving the lines of 

 force in a bar-magnet to run spirally round the bar between the 

 equator and poles, the equator being decentred and oblique across 

 the bar, as shown by diagrams. — Prof. Rowland, of Baltimore, 

 made some observations on the new theory of terrestrial mag- 

 netism of Professors Ayrton and Perry. He said the experiments 

 on which the theory was founded had been attributed to Helm- 

 holtz, but they were entirely his own, he having gone to Berlin 

 to make them. The new theory had occurred to himself on 

 making these experiments, but he had rejected it because he 

 found that the potential which the earth's surface would require 

 to have would not only cause violent planetary disturbances, but, 

 by mutual repulsion, drive objects off the earth. He had made 

 also an experiment to see if absolute motion of electricity would 

 cause magnetisation, but failed to get any effect from it. Then 

 he resorted to calculation to find the magnetic effect of relative 

 motion by rotation of a charged sphere of perfect magnetic per- 

 meability that is more magnetic than iron. He found that when 

 the sphere was uniformly charged and rotating there would be a 

 magnetic field in its interior ; but instead of the result of Messrs. 

 Ayrton and Perry, that if the earth were charged to a potential 

 of, he believed, 10' volts relatively to interplanetary space, the 

 earth's magnetism would be what it is, he found the neces- 

 sary charge to be 61 X 10" volts. In the ordinary atmo- 

 sphere this potential would produce a spark nine million 

 miles long and discharge across to the moon. If the moon 

 were electrified to the same degree the mutual repulsion 

 would overcome the force of gravity between them. He there- 

 fore considered terrestrial magnetism to be still a 'mystery. 

 He had also thought that the aurora borealis might be explained 

 by supposing the upper regions of the earth's atmosphere electri- 

 fied. The winds carrying the upper strata towards the poles, 

 electricity would condense there. This hypothesis was still ten- 

 able. Prof. Ayrton said that whether or not the new theory of 

 magnetism should be so rejected depended on whether or not 

 Prof. Rowland's calculations, or those of himself and Prof. 

 Perry were wrong. It had been found by Sir William Thom- 

 son, from experiments at Arran, that the earth was electrified 

 with respect to the air, and that there is a difference of 

 potential of 30 volts between earth and air for each foot of 

 ascent. This gave 1360 X to'^ centimetre-gramme-second 

 electrostatic units as the potential of the earth. The new theory 

 required the potential to be loi l X 10", supposing the earth to 

 be of solid iron, or about fourteen times more — a wide margin. 

 Prof. Rowland said he had not seen the calculations of Professors 

 Ayrton and Perry yet, but he believed his results to be correct, 

 as he had checked them in various ways. — Mr. Bailley exhibited 

 a modification of Arago's experiment, in which a copper disk is 

 caused to rotate continuously by changing the polarity of four 

 electro-magnets underneath by a revolving commutator. — Mr. 

 Conrad Cooke exhibited a single voltaic element showing the 

 internal current. This is done by forming the glass vessel con- 

 taining the element into a helical tube between the poles, and 

 hanging a galvanometer needle in the interior of the helix ; 

 the internal current deflects the needle. "' 



Geological Society, June 25. — Prof. P. Martin Duncaifi 

 F.R.S., vice-president, in the chair. — Edward Garlick was 

 elected a Fellow of the Society. — The following communications 

 were read : — On the evidence that certain species of Ichthyosaurus 

 were viviparous, by Prof. H. G. Seeley, F.R.S., F.G.S. — On 

 Rhamphoctphalus prestwUhi, Seeley, an Ornithosaurian from the 

 Stonesfield Slate of Kineton, by Prof. H. G. Seeley, F.R.S.— 

 A contribution to South American geology, by George Attwood, 

 F.G.S. The paper describes a line of country in Spanish 

 Guayana, Venezuela, S.A., commencing from a small town 

 called " the Porfof Las Tablas," on the Orinoco River, ex- 

 tending about 1 50 miles, and consisting of a series of crystalline 

 and altered rocks. Syenite is the first rock met with, and then 

 are found granite, quartz-diorite, hcematite, and magnetic iron 

 ores, gneiss, slaty rocks, gabbro, and diabase. In the diabase 

 the quartz veins are found to contain large quantities of gold 

 mixed with the vein matter ; the alluvial soil in the neighbour- 

 hood of the quartz veins also contains gold nuggets and small 

 grains of gold. Although quartz veins are found in great 

 numbers from the river to the interior, none of them have so far 



