August i6, 1900] 



NA TURE 



;69 



as to be under the influence of a magnetic field, is broken up into 

 two circular components oppositely polarised. 



The system used consisted of two rectangular prisms of glass 

 placed with their diagonal faces parallel and separated by a 

 plate of mica of approximately \ \ retardation. The lines of 

 force were parallel to this plate. A ray of ordinary light from a 

 sodium flame sent into the system normal to this plate was 

 successively totally reflected parallel to the lines of force and 

 then at right angles to the mica, which served to change the 

 phase and to keep the absolute direction of the circular vibra- 

 tions the same. The rays passed five times around within this 

 system, giving twenty internal reflections. 



The separation of the rays agreed, so far as could be deter- 

 mined, with the calculations based on the assumptions usually 

 made in explaining this phenomenon. When the field was 

 reversed, the direction of vibration of each circular component 

 was reversed. This does not establish the assumption of a rela- 

 tive change in the velocities usually made, as a relative change 

 in the phase of the components, or both, would produce the same 

 effect. It does show, however, that a medium in a magnetic 

 field transmits, in the direction of the lines of force, light 

 vibrations by circular components only. D. B. Brace. 



Physical Laboratory, University of Nebraska, August I . 



Physical Structure of Asbestos. 



Can any of your readers tell me where I can find a good 

 account of asbestos and its physical structure? The ordinary 

 works of reference I am acquainted with give too meagre an 

 account to be of any use. GEOFFREY Martin. 



13 Hampton Road, Bristol, August i. 



THE BRADFORD MEETING OF THE 

 BRITISH ASSOCIATION. 

 T T is now possible to give a forecast of the chief 

 -*• subjects to be brought before the various Sections 

 of the British Association at the forthcoming Bradford 

 meeting. The following outlines of sectional pro- 

 grammes show that many matters of importance and 

 wide scientific interest will be dealt with, so that the 

 Bradford meeting promises to be a memorable one. 

 No particulars as to the probable proceedings of the 

 Physics Section have yet been received. 



Chemistry. 



Prof. W. H. Perkin, jun., F.R.S., the President of 

 Section B (Chemistry) is this year setting a precedent 

 in the conduct of the sectional meetings. Several 

 members of the Association have been asked to furnish 

 reports on the present state of knowledge in the parti- 

 cular departments of chemistry with which they are 

 especially conversant, and the reading of these reports 

 will be followed by discussion. 



In accordance with this programme, Mr. Francis H. 

 Neville, F.R.S., will present a report dealing with the 

 properties and interactions of the metals. The following 

 questions will be brought forward for discussion in 

 connection with the report : — 



1. Are the methods usually employed in studying the 

 equilibrium between two or more substances with change 

 of temperature immediately applicable to the study of 

 alloys, and are similar results obtained in the two cases ? 

 Thus, with varying conditions of temperature and con- 

 centration, a system of ferric chloride and water deposits 

 (i) ice; (2) Fe2Cl,„i2H.,0 ; (3) Fe.>CI,i.7H.,0 ; (4) 

 Fe.,Cle,5H.p ; (5) FeXI,, 4H2O ; (6) Fe;CI„ or "(7) mix- 

 tures of the phase numbered n with that numbered 

 (« -h i) ? Are the solubility curve of ferric chloride and 

 the freezing point curves of metallic mixtures of the same 

 kind? 



2. How far does (i) microscopic examination, and 

 (2) change in physical properties, such as electromotive 

 force, &c., enable us to detect the existence of a compound 

 in an alloy? 



NO. 1607, VOL. 62] 



3. In what definite proportions are metals known to 

 combine ? Is any regularity manifest with respect either 

 to their position in the periodic system or to their valency 

 with regard to non-metals ? 



4. What methods are available for determining the 

 molecular weights of the metals, and can it be asserted 

 in any cases, other than those of mercury, zinc and 

 cadmium, that the molecular weight is satisfactorily- 

 determined ? 



5. Can a definition be given of a metallic element 

 which makes it possible to distinguish between metals 

 and non-metals ? 



6. Can any explanation be given which will satis- 

 factorily account for (i) the difference between metallic 

 and electrolytic conduction, and (2) the remarkable 

 changes in the electrical conductivity of metals attending 

 admixture ? 



As some of the questions bearing upon this subject 

 are of as great importance to the physicist as to the 

 chemist, physical members of the Association are to be 

 invited to join in the discussion. Dr. Adolf Liebmanti 

 will contribute a report on recent improvements in the 

 treatment of textiles, a subject which acquires peculiar 

 importance from the fact that the 1900 Meeting of the 

 Association is being held in the centre of a district 

 devoted to the textile industry. Dr. Arthur Lapworth 

 will give a report on our knowledge of the chemistry 

 and constitution of camphor. Attention has of late 

 years become so concentrated on the chemistry of the 

 camphor group as to make an authoritative discussion on 

 the constitution of camphor almost a necessity to the 

 organic chemist. Mr. William J. Pope will present a 

 report on our present knowledge of stereochemistry ; it 

 is understood that special attention will be given in this 

 report to the work done during the past twelve months 

 on the optical activity of compounds containing an 

 asymmetric nitrogen, tin or sulphur atom. Among the 

 other papers to be presented at the meeting is one on 

 the specific heat of gases at temperatures above 400% 

 by Prof. H. B. Dixon, F.R.S. ; and Mr. H. T. Brown, 

 F.R.S., will give an account of his recent work on the 

 diffusion of gases and liquids. The papers of special 

 local interest include one on the treatment of Bradford 

 sewage, by Mr. F. W. Richardson, the City analyst ; 

 and also a paper on the treatment of woolcombers' 

 effluents, by Mr. W. Leach. The title of the sectional 

 address to be delivered by the President is, of course, not 

 yet announced ; it is understood, however, that the address 

 will deal with the teaching of chemistry. 



Geology, 



The proceedings of Section C (Geology) will open at 

 10.30 a.m. on Thursday, September 6, with the delivery 

 of the address of its president. Prof. W. J. Sollas, who 

 has chosen for his subject, " The History of the Earth in 

 relation to a Scale of Time." Prof. Sollas will take a 

 wide scope in discussing this subject, and will introduce 

 such fundamental matters as the constitution of the 

 earth, the relative value of the various geological periods, 

 the origin .of ocean basins, the formation of mountain- 

 chains, and the evolution of the organic world. We may 

 be sure that his discourse will be brilliant and suggestive. 

 It is probable that Prof J. Joly will also treat on the 

 knotty problem of the duration of geological time at the 

 same, or a subsequent, meeting of the Section. 



As befits the place of meeting, the geology of the 

 Carboniferous rocks will receive much attention. A joint 

 discussion with the botanists (Section K), on the con- 

 ditions which existed during the growth of the forests of 

 the Coal Period, will be held on Monday, September 10, 

 when Mr. A. Strahan and Mr. J. E. Marr will open the 

 debate from the geologist's standpoint. The Coal- 

 measures of the West Riding form the subject of a paper 

 by Mr. W. Cash, and those of North Staffordshire of one 



