Oct. 6, 1887] 



NATURE 



549 



this thickness. The authors conclude that in all probability the 

 whole phenomenon is due to the surfaces being separated by 

 these short distances. 



On the Magnetic Properties of Gases, by Prof. Quincke, Ph.D. 

 — A few years ago he invented what he called a magnetic 

 manometer. It consists of a bent tube, of which one limb is 

 much wider than the other. In the wide limb is the gas to be 

 experimented on. The narrow limb and the connecting hori- 

 zontal piece contain liquid, and the difference of level of the 

 liquid in the narrow limb produced by the magnetic field is 

 what is measured. 



The magnetic pressure per unit of area is given by the 

 formula — 



R 



\i h be the difference of level of the liquid in the two limbs, i.e. 

 the hydrostatic pressure, we have — 



h<T = 



R - R, 



H,2. 



The smallest diamagnetic constant for the gases experimented on 

 was found to be that of hydrogen. Oxygen had the highest. 

 He compares his results with Faraday's, and finds that they 

 agree substantially, the differences being probably due to im- 

 purities. 



Pinal Value of the B.A. Unit of Electrical Resistance as 

 determined by the American Committee, by Prof H. A. Row- 

 land. — His determination in 1876 gave I B.A. unit = '9878 

 ohm. For his present determination the apparatus was on a 

 very large scale. He employed both the Kirchoff and the 

 Lorenz method. By the former method he got a final value of 

 •98646 ± 40, by the latter a value of "9864 ± 18 ; so that the 

 latter method has a probable error of less than a half that of 

 the former. His value for the resistance of 100 cubic centi- 

 metres of mercury came out "95349 B.A. units. 



Lord Rayleigh said that the results showed that the absolute 

 letermination of the B.A. unit by various experiments agreed 

 much better than the comparison with the mercury standard. 

 This was exactly the opposite of what he would have expected. 

 Prof. Rowland had suggested that one cause of the difference 

 I)etween their determinations of the mercury standard might be 

 that in the American experiments the tubes had been mechanic- 

 ally w^iped, so that there was no chance of dust remaining in 

 them. He hardly thought, however, that this was likely. The 

 want of uniformity in the diameter of the tube might possibly 

 have an effect. 



On Induction between Wires and Wires, by W. H. Preece, 

 F.R. S. — A continuation of a subject brought before the 

 Association last year, when it was shown that electro-magnetic 

 disturbances extended to distances much greater than was 

 imagined, and that effects were observed across many miles of 

 country. Experiments were made on the banks of the Severn 

 and Mersey, on the Portcawl Sands of South Wales, in the 

 fields in the neighbourhood of Cardiff, on the roads and rail- 

 ways of Oxfordshire, Worcestershire, and Shropshire, in the air 

 and under water, in the corridor of the General Post Office in 

 London ; and the l,aw was formulated that the distance depended 

 directly on the strength of the currents inducing the disturbance 

 and on the length of the wires opposed to each other, and 

 inversely on the square of the distance separating them, and on 

 the electrical resistance of the disturbed wire. 



The influence of i mile of wire carrying i ampere of current 

 can apparently extend to a distance of i "9 mile. The law is 

 given by the following formula : — 



C — Ml 



where C^ is the primary current, Cj the secondary, / the length 

 of the wires opposed to each other, d the distance separating 

 them, r„ the resistance of the secondary circuit. When these 

 quantities are represented in C.G.S. units, M equals '005. 

 The current induced by i mile, of i ampere at i mile distant is 

 1*3 X 10-" ampere. A current is still perceptible at I "9 mile 

 distant ; hence we can calculate that a Bell telephone requires 

 six ten-thousand-millionths of a milliampere, or, in figures, 

 ■0000000006 milliampere, to be audible. 



One curious result of these inquiries is that the disturbances 



are transmitted equally well through water and the earth as 

 through air, and hence our cables are disturbed as well as our 

 land wires. Communication with coal-pits is possible, though 

 nothing but the earth intervenes. 



On the Effect of Continental Lands in altering the Level of 

 the adjoining Oceans, by Prof. Edward Hull, F.R. S., Director 

 of the Geological Survey of Ireland. — The effect of the attrac- 

 tion of continental lands upon the oceanic waters adjoining 

 seems to have been very much overlooked by British physical 

 geographers. That some slight effect arises in the direction of 

 elevating the surface of the ocean in proximity to the coast is 

 generally admitted, but the amount of rise is considered to be 

 small, perhaps insignificant. The prevalence of these views 

 was attributed by the author to the widespread influence of 

 Lyell's hypothesis of the uniformity of the ocean-surface all over 

 the globe. 



The author proceeded to discuss the effect of continental lands, 

 showing that this was in the first instance divisible under two 

 principal heads : The effect (i) of the unsubmei^ed, and (2) of 

 the submerged masses. In the former case, where the mass 

 rose above the surface, one component of the attraction acted in 

 a more or less vertical direction ; in the second case, all in a 

 lateral direction ; but both had the effect of elevating the surface 

 of the ocean. The horizontal distance to which the vertical 

 effect extended owing to the curvature of the earth's surface 

 was then considered : and it was shown that, where con- 

 tinental lands rise from a deep ocean, the effect of the lateral 

 attraction far exceeds that of the vertical attraction of the un- 

 submerged mass. Prof. Stokes has furnished the author with a 

 hypothetical case, in which the elevation of the ocean was 

 estimated to reach 400 feet above the mean geodetic surface of 

 the earth. 



For the purposes of illustration three cases were selected, 

 viz. : — 



(i) The table-land of Mexico, between lats. 18° and 26" N. 



(2) The table-land of Bolivia, ,, 19' and 26" S. 



(3) The Andes of Chili, ,, 26° and 35° S. 

 The mean elevations, distances from the ocean, and extent 



having been determined, and the mean density of the crust being 

 taken at 2*6 for emergent, and I "6 for unsubmerged land, the 

 results of the attraction of the mountain masses in each case 

 were as follows : — 



(i) Mexico, 780 feet j (2) Bolivia, 2160 feet ; (3) Chili, 1580 

 feet. 



The total calculated rise of the ocean-waters at a distance of 

 900 miles from the coast in lat. lo° S. would amount to 2568 feet. 



The above results, which are probably rather under than over 

 estimates, fall considerably short of those to be drawn from 

 Suess and Fischer's formula, but are probably much in excess of 

 the views held by British physical geographers generally ; and 

 the conclusion was drawn that if the same processes of reasoning 

 and calculation were applied to all parts of the world, it would 

 be found that the ocean waters were piled up to a greater or 

 less extent all along our continental coasts, producing very im- 

 portant alterations in the terrestrial configuration as compared 

 with an imaginary ellipsoidal, or geodetic, surface, to which all 

 these changes of level must necessarily be referred. 



On a Standard Lamp, by Prof. A. A. Vernon Harcourt, 

 F. R.S. — At one of the meetings of this Section last year a lamp 

 devised by the author for producing a constant amount of light 

 was shown and described by Mr. W. S. Rawson. The lamp 

 now exhibited serves the same purpose, but is simpler in 

 principle, more easily adjusted, and less affected by draughts. 

 It consists of a glass reservoir with tubulure and stopper of the 

 form and size of a large spirit-lamp, mounted on a metal stand 

 provided with levelling screws. The wick can be turned up 

 and down in the normal manner within a long tube attached to 

 the body of the lamp. Round this tube is a wider tube 

 100 X 25 mm., and the two being joined together above and 

 below by flat plates constitute the burner of the lamp. When 

 the burner becomes warm by conduction of heat from the flame 

 of the lamp, the pentane in the wick volatilizes and burns at a 

 considerable distance above the point to which the wick is 

 turned down. Thus the size, or texture, or quality of the wick 

 does not affect the flame. Around the burner and the lower 

 part of the flame is another cylinder open at both ends and con- 

 tracted above the burner to a tube 21 mm. in diameter. A 

 similar tube forms the lower part of an upper chimney, which is 

 enlarged above to a diameter of 25 mm. The upper part of the 



