September 26, 1895] 



NA TURE 



a syllabus of examples. This suggestion was adopted by the 

 Section. 



The range of subjects included in the work of the Section was 

 perhaps nowhere better exemplified than in the passage to the 

 next paper, a report on cosmic dust, by Dr. J. Murray. An 

 examination of the red clay from the bottom of the Pacific 

 Ocean, in places looo miles from any coast, enables three classes 

 of magnetic particles to be distinguished ; these are — crystalline 

 fragments of magnetic or titanic iron, dark shiny spherules con- 

 taining metallic iron, and the browni.sh spherules known as 

 chondres. The various layers of manganese nodules found 

 surrounding nuclei of tertiary teeth or bones contain these black 

 and brown spherules, and there is every indication that the 

 brown ones are of extra-terrestrial origin. In this case they 

 ought to occur at all, or at any rate many, points on the earth's 

 surface ; Dr. .Murray has, however, looked for them in vain both 

 in the dust of Greenland glaciers and on the summit of Ben Nevis. 

 He is of opinion that the accumulation of meteoric dust takes 

 place with exceeding slowness, say about 20 lbs. of dust per 

 square mile per century, and that the bed of the Pacific Ocean 

 has not received one foot of deposit since the tertiary period. 

 Consequently any attempt to gather these particles will probably 

 be fruitless, unless continued over a long period, lie wished (or 

 suggestions as to the best method of procedure in the future. It 

 was pointed out that a good opportunity for the collection of 

 meteorites will be afforded by the meteor shower 0.' November 

 1899. 



The Committee on underground temperature have been for- 

 tunate this year in obtaining records from a bore-hole in New- 

 South Wales, the first observations made in the southern hemi- 

 sphere. The bore-hole is situated near Port Jackson, close to 

 Sy<lney Harbour ; it is 2929 feet deep, and contains water. The 

 ^;radient observed was a small one, being a rise of 1° F. in 

 descending 80 feet vertically. The observers suspected that the 

 temperature of the rock was influenced by the proximity of the 

 water in the harbour, but an examination of the temperature 

 distribution in the harbour did not confirm this. Lord Kelvin 

 suggested the .Vfrican mines as a new field for observations. 



Prof. S. P. Thompson reported the recommendations of the 

 Committee on the size of pages of scientific periodicals. It is 

 considered advisable to retain quarto and octavo sizes, and 

 certain limits for text and margin are given for each of these 

 sizes. There appeared to be a strong feeling against any change 

 in the sizes of the Royal Society's publications. During the 

 year the Committee will endeavour to induce other scientific 

 societies to adopt the standard sizes recommended. 



Prof. Riicker communicated the results of a comparison of 

 magnetic standard instruments, made by himself and Mr. W. 

 Watson. In his presidential address to the Section last year he 

 showed that it was useless to proceed further with a magnetic 

 .survey until a direct comparison of standards used in the various 

 observatories had been made, because it was well known that 

 instruments diftered greatly. During the year he has visited 

 the various magnetic observatories, carrying a portable declino- 

 meter of the Kew pattern, and with Mr. Watson's assistance has 

 directly compared the simultaneous readings of his declinometer 

 and that of the observatory-. Errors are found in the latter, 

 which are in every case traceable to magnetic material in or on 

 the wooden box containing the suspended magnet. If this box 

 be replaced by an ebonite one, the error disappears. It is, how- 

 ever, easier to allow for the error than to get rid of it ; its 

 amount is perfectly definite. 



On Friday the Section sat jointly with .Section B. Lord 

 Rayleigh read a paper on the refractivity and viscosity of 

 these gases. He described how, by means of an electric arc, 

 kept up for several weeks in a mixture of oxygen and atmo- 

 spheric nitrogen, he finally obtained more than a litre of argon 

 at atmospheric pressure. This proved to have the same density 

 as the specimen obtained by the magnesium method. The re- 

 fractive index was measured by the interference method of 

 Fizeau, the two beams being separated by slits in front of the 

 lens nearest the eyepiece. The latter was constructed of cylin- 

 drical lenses. To avoid the use of cross-wires, the tubes con- 

 taining the gases under comparison were arranged .so as not to 

 occupy ihe whole field of view, some light passing parallel to, 

 and outside Ihem ; two sets of fringes were thus obtained, which 

 could be brought to coincidence by varying the pres.sure of either 

 gas. .\djustments were made for several pressures, one of the 

 tubes always containing air. The values of the refractivity (;i - i) 

 were, for argon 0-961, and for helium 0-146, that of air being 



taken as unity. The viscosity of each gas was measured by its 

 rate of flow through a capillary tube, the results being (air=l) 

 argon I '21, helium 0-96. Lord Rayleigh mentioned that a 

 sample of nitrogen collected from a Hath spring, where it bubbles 

 out along with the water, give the D3 line of helium. Dr. 

 Gladstone showed that the results of these experiments assign 

 to argon the atomic weight 20, its specific refractive energy- 

 being intermediate between those of fluorine and sodium, but 

 not between those of potassium and calcium. 



Prof. Schuster then opened a discussion on the evidence to be 

 gathered as to the simple or comjxjund character of a gas from 

 the constitution of its spectrum. Recent spectroscopic work in 

 connection with argon and cleveite gas has directed attention 

 to the double spectra exhibited by these substances, and 

 conjectures have been made that the two spectra indicate the 

 gases to be mixtures. Prof Schuster expressed strongly the 

 view that gases with double spectra are not necessaril)' 

 mixtures or compounds. He quoted in support of this the 

 cases of sodium and mercury vapours, and oxygen, in all 

 of which the absorption spectrum differs from that of the 

 luminous vapour. The difticulty is not explained by assuming 

 dissociation to occur, because some substances have three or 

 more spectra. He thought mere examination of spectra would 

 not suffice to determine whether an unknown substance is an 

 element, mixture of elements, or compound. 



The despondent view of Prof. Schuster was not shared by 

 Prof. I-tunge, of Hanover, who at this point contributed an ac- 

 count of the researches of himself and Prof. Paschen on the 

 spectrum of cleveite gas, showing that it is a mixture. (.\n 

 account of this work by the authors themselves will be found on 

 p. 520.) 



Dr. G. J. Stoney contributed to the discussion by a paper on 

 the interpretation of spectra. 



On Saturday the Section was subdivided into two departments, 

 mathematics and meteorology. 



In the department of mathematics. Lord Kelvin read a paper 

 on the translalional and vibrational energies of vibrators after 

 impacts on fixed walls, in which he sought to find an exception 

 to the Maxwell-Boltzmann theorem relating to the average trans- 

 lational energy of the molecules of a gas. He calculated the 

 time-average of the translalional energy of a free particle after 

 coming into contact with a vibr.ating particle, and found it 

 always in excess of that which would be given by the Maxwell- 

 Boltzmann law-, though approximating more nearly to that 

 average when the number of encounters was considerable ; and 

 that it seemed ultimately to give a total average out of accord- 

 ance with the law. In the di.scussion which followed, Mr. G. H. 

 Bryan pointed out that the Maxwell-Boltzmann law referred to 

 the statistical average energy of a great number of particles, not 

 to the time-average energy of a single particle. 



Prt>f. Hicks, in his ])aper on a spherical vortex, stated that he 

 had proved the possibility of building up a compound spherical 

 vortex consisting of successive shells in which the rotation Ls 

 oppositely directed, the vorticity and size of each shell satisfying 

 a definite relation. In a paper on bicyclic vortex aggregates, he 

 stated that it was possible, with given current and vortex-sheets, 

 to have a steady j;//rrt/ motion round an axis, compounded of 

 motion in planes through the axis and motion in circles round 

 the axis, the cyclic constants of the two component motions 

 being independent of each other. 



Mr. G. T. Walker showed an ingenious top in the shape of 

 a flattened ellipsoid in which rotation could become converted 

 into oscillations, and vice versd, by means of an adjustable piece 

 which could be arranged unsynmietrically. 



Dr. Burton made some suggestions as to matter and gravitation 

 in the cellular vortex ether described in Prof. Hicks"s presidential 

 address. 



Mr. P. H. Cowell read an important paper on recent develop- 

 ments of the lunar theory, chiefly by Dr. G. W. Hill, extended 

 in the current number of the Aiiicricaii Journal by an admirable 

 paper by Prof. E. W. Brown. The order of work in attacking 

 problems in the lunar theory- is quite altered and much simplified 

 in the new method. In a short discussi(m which followed, Mr. 

 Cowell stated that Prof Brown was engaged in bringing out a 

 treatise on the lunar theory. 



Prof. J. D. Everett read a paper on absolute and relative 

 motion ; and Mr. W. H. Everett made a communication on the 

 calculation of the magnetic field due to a current in a solenoid. 



In pure mathematics, Major MacMahon gave an interest- 

 ing method of graphically representing partitions of numbers. 



NO. 1352, VOL. 52] 



