622 



NA TURE 



[April 27, 1899 



turbances are taking place in the dielectric envelope. An ex- 

 pression is given for the maximum value of the magnetic induc- 

 tion when the sphere becomes an infinite plate and the inducing 

 system consists of an alternating current in a circular circuit 

 whose plane is parallel to the plate, i.t. when the maximum 

 value of the induction tangential to the surface is zero. A second 

 expression gives the maximum value of the magnetic induction 

 normal to the surface for a point at considerable distance from 

 the axis, and just outside the plate. In this latter case, the 

 maximum value of the induction tangential to the surface appears 

 as a function of the maximum current of known frequency in 

 the inducing circuit, the various dimensions in space of the 

 system, and the permeability and specific resistance of the plate. 

 From these equations, taking the most authentic values of the in- 

 volved constants, the maximum magnetic induction normal to the 

 surface for a sea-water plate is forty-four times as great as it would 

 be for an iron plate, and more than three thousand times as great as 

 it would be for a copper plate. The paper also shows that, for 

 the purpose of induction telegraphy, to get the best effect the 

 receiving coil should have its plane vertical, not horizontal, 

 firstly because the distance of the inducing circuit from the sur- 

 face of the plate must in practice be small compared with the 

 distance of the point from the axis, so that the maximum normal 

 induction is small compared with the maximum tangential induc- 

 tion; and secondly because the maximum 7!orw;a/ induction varies 

 inversely as theyf/i'/i power of the distance of the point from the 

 axis, whereas the maximum tangential induction varies inversely as 

 the fourth power of that distance. In conclusion, Mr. White- 

 head applies his formula to the practical case mentioned by 

 Prof. Lodge in the fournal of the Institute of Electrical 

 Engineers, February 189Q, p. S05. Prof. Lodge there describes 

 a horizontal receiving circuit, and states that, with no' con- 

 densers in the circuit he "was not usually able to hear any- 

 thing " in the telephone. Mr. Whitehead calculates that under 

 such conditions the theoretical value of the current in Prof. 

 Lodge's horizontal secondary is 0'066 /w/Vra-amperes, but that 

 with a vertical circuit the received current would have been 33 

 ///////-amperes. Mr. Blakesley observed that as a rule experi- 

 ment preceded theory. He congratulated Mr. Whitehead upon 

 having settled from theoretical considerations that the vertical 

 position of the receiving coil is best. Prof. Everett said that 

 the very elaborate method of analysis adopted in the paper 

 appeared to be very clearly stated. He would like to know 

 whether the inducing coil ought to be vertical as well as the 

 receiving coil. Mr. Appleyard thought that experiment had 

 left no doubt as to the best position of both coils. The early 

 investigations of Mr. Willoughby Smith and the later work of 

 Mr. H. R. Kempe and Mr. Preece had proved that for the best 

 effect both coils should be vertical. But large vertical coils 

 were difficult to fix and expensive to maintain. It was this 

 reason probably that led Prof. Lodge to try what could be done 

 with coils placed horizontally Mr. Whitehead, in reply, said 

 that his formulce only applied to a horizontal inducing coil. He 

 had not worked out the case of what would happen if the 

 inducing coil itself was vertical. In the experiments on the 

 Flat Holm both circuits were straight wires with their ends 

 to earth, so that they really amounted to vertical coils. — 

 Mr. R. A. Lehfeldt then gave a demonstration of a method due 

 to Prof. T. W. Richards i'ix standardising thermometers. This 

 depends upon the ordinary latent-heat principle for maintaining 

 constant temperature, but it includes the consideration of gener- 

 ally more than two states or phases of the melting substance. 

 If there are f components and / phases, then the number of 

 degrees of freedom of the system is [1 -I- 2 - /]. When this is 

 zero, the temperature and the pressure of the system are perfectly 

 definite. Thus the following chemical formula represents the 

 four phases to be equilibrated in the case of Glauber's salt : 



/Na,SO^loH..O 

 I Na-jSO^ 

 I Solution 

 (.Vapour. 



Prof. Richards has determined the temperature of equilibrium in 

 several useful cases. The salts are put into a test-tube in an air- 

 bath formed between it and a second test-tube ; the whole is 

 then heated in a beaker of water over a sm.ill flame. If the 

 salt is pure, and care is t.aken to avoid the effect of supers-atura- 

 lion. this method is highly satisfactory. It gives an extensive 

 range of fixed-points, and is especially useful in thermometry for 



NO. 1539. VOL. 59] 



A few of these temperatures 



•c 



1971 



53'3 



48-0 



508 



57-8 



734 



780 



fixed-points between 0° and 100°, 

 may be noted : 



Sodium chromate 

 Sodium carbonate 

 Sodium thiosulphate 

 .Sodium bromide 

 Manganese chloride 

 Trisodium phosphate 

 Barium hydroxide 



Mr. J. A. Harker asked how long the temperature remained 

 constant. The special value of Richards' method for standard- 

 ising thermometers of short range had been pointed out by Dr. 

 Chree. It obviated the necessity for auxiliary bulbs, and it 

 would be extremely useful in graduating meteorological ther- 

 mometers. Mr. Blakesley said that sodium chromate was repre- 

 sented by a very useful temperature. Could this substance be 

 regarded as sutticiently stable to give a satisfactory fixed-point. 

 Mr. Lehfeldt, in reply, said that all the fixed-points mentioned 

 were theoretically as definite as that corresponding to sodium 

 sulphate, but they had not been so accurately determined. 



Geological Society, April 12. — W. Whitaker, F.R.S. 

 President, in the chair. — Mr. A. M. Davies, in exhibiting a 

 specimen of glauconitic limestone from the Kimeridge clay, 

 said that it might easily be taken for upper greensand. There 

 are traces of fossils in the stone, but an impression of a biplex 

 ammonite was alone recognisable. No similar bed had been 

 previously recorded from the English Kimeridgian. — Fossils in 

 the University Museum, Oxford: (l) Silurian echinoidea and 

 ophiuroidea, by Prof. W. J. Sollas, F.R.S. Attention is called 

 to the correlation of structure and function in the locomotive 

 organs of asterids, ophiurids, and echinids. — Note on the occur- 

 rence of sponge-spicules in the carboniferous limestone of 

 Derbyshire, by Prof. W. J. Sollas, F.R.S. Remains of sponge- 

 spicules are fairly abundant in a rock-slice taken from a specimen 

 obtained by Mr. H. II. Arnold-Bemrose from Tissington cutting. 

 They present them,selves as sections through long cylindrical 

 rods, but the terminations are obscure and indefinite, and the 

 form cannot be referred with certainty to any recognised order 

 of sponges. The spicules were doubtless originally siliceous, 

 but they are now completely transformed into carbonate of lime. 

 — On spinel and forsterite from the Glenelg limestone, byC. T. 

 Clough and Dr. W. Pollard ; communicated by permission of 

 the Director-General of H.M. Geological Survey. The paper 

 opens with an account of previous literature on the subject of 

 minerals in the tllenelg limestone. Neither forsterite nor true 

 spinel has been previously recorded from the limestone or from 

 Scotland at all. The forsterite and spinel are in part asso- 

 ciated together in lumps, from which they were separated by 

 means of heavy solutions for analysis. The spinel in hand- 

 specimens is of an almost opaque blue colour, and some ex- 

 amples show- small crystal-faces. That seen in microscopic 

 slides is shapeless and colourless, except that the blue portions 

 appear brown liy transmitted light. Analyses of the two 

 minerals are given at the close of the paper ; and it is pointed 

 out that the spinel is like that of Aker in colour and mode of 

 occurrence. 



Mineralogical Society, April 11. — Mr. R. II. Scott, Past- 

 President, in iIr- chair. — Mr. F. R. Mallet gave the results of 

 the examination of a mineral obtained many years ago from the 

 Mayo salt mines, Punjab: he proves it to be L;ingbeinite, sulphate 

 of potassium and magnesium K.jSOi.2MgSOj), a species first es- 

 tablished in I S91 from material found in the Prussian salt deposits. 

 — Mr. L. Fletcher gave an account of a mass of meteoric iron from 

 Patagonia, a fragment of which had been brought to this country 

 by Dr. F. P. .NJoreno of La 1'l.ata ; the material contains nearly 

 10 per cent, of nickel and colalt, and belongs to the class of 

 octahedral meteoric irons, like that of Toluca. — Mr. G. F. \\. 

 Smith read a paper on the use and advantages of a three-circle 

 goniometer. The older form of goniometer with one circle 

 has the grave disadvantage that the crjstal must be re- 

 adjusted for different zones. In the case of the theodolite 

 goniometer with two circles, the crystal is adjusted once 

 for all, and measurements are made of the polar distance and 

 azimuthal angle of each face ; but by this method no use can be 

 made of the l.nv known as the anharmonic ratio of four (xjles in 

 a zone, and in fact the indices of faces are not readily determin- 



