March ii, 1886] 



NA TUR£: 



453 



own lectures and those of Prof, von Koeneu, Professor of 

 Geology. 



From tbis it is evident, as Prof. Wagner concludes, " that 

 there is no connection whatever {gar kein Konnex) between my 

 lectures and those of the geologist." 



Can any one doubt that the establishment of such a system 

 of teaching geography and geology, side-by-side, as set forth in 

 these two communications, would not be of the utmost benefit 

 to our country and its education generally, if established in our 

 Universities also ? It will be impo'^sible to obtain adequately 

 trained teachers of physical geography until such courses of in- 

 struction are open ; and until adequately trained teachers are 

 produced for higher schools and training colleges, no real pro- 

 gress in the teaching of physical geography can be made through- 

 out the country. 



There can scarcely be a doubt that the establishment, at our 

 Universities, of such a condition as that at the German ones, 

 would be in every way to the advantage and advancement of 

 geology, and to the increase of the numbers of its students ; it 

 would also advance the cause of all other branches of natural sci- 

 ence, and all interested in the teaching of these subjects ought to 

 support a movement in favour of its adoption warmly. No 

 doubt the adoption of the system is merely a question of time, — 

 England cannot lag behind in the study of geography for ever. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE 



Cambridge. — Mr. J. E. Marr, M.A., Fellow of .St. John's 

 College, has been appointed University Lecturer in Geology. 



It is estimated that the ethnological collections now displayed 

 in the Antiquarian Museum are worth at least 2000/., and with 

 a little additional accommodation objects valued at looo/. more 

 i-an be displayed. These series are of inestimable value to the 

 student of anthropology, and from the labours of Baron von 

 Iliigel in their arrangement the University is reaping a rich 

 harvest. The baron contemplates illustrating them by a full 

 series of maps and drawings. 



The honorary degree of M.A. is to be conferred on Mr. C. 

 Todd, Government Astronomer, Postmaster-General, and Di- 

 rector of Telegraphs in South Au-tralia. 



The Open Entrance Scholarships for Natural Science to be 

 competed for in the ensuing months include those of Peterhouse, 

 Chemistry and Physics, October ; Clare, Natural Science, 

 March 24 ; Downing, Natural .Science, June i ; Non-Collegiate 

 Students, Physical Science, July. 



Mathematical Scholarships will be given at each College men- 

 tioned above (e.tcept Downing), and at Trinity Hall, March 17 ; 

 Corpus Christi, March 23 ; Queens', April 27 ; St. Catherine's, 

 May II ; Magdalene, March 17. Further information will be 

 given by the Tutors of each College. 



At the City and Guilds of London Institute, Central Institu- 

 tion, Exhibition Koad, S.W., Prof. Ayrton, F.R. S., will give a 

 course of six lectures on some of the industrial applications of 

 electricity, from 5 p.m. to 6 p.m. Friday afternoons, March 12, 

 19, 26, April 2, 9, and 16. The lecture on March 12 will be 

 im Electric Lighting ; March 19, Electricity as a Motive Power; 

 March 26, Klectric Storage of Energy ; April 2, Electric Trans- 

 mission of Power ; April 9, Electric Meters; April 16, Electric 

 Locomotion. 



At Clifton College a .Scholarship of the value of 30/. per 

 annum, tenable for three years at the Central Institution of the 

 City and Guilds of London Institute for the Advancement of 

 Technical Education, is offered by the Committee of the 

 Institute, and will be awarded, on the nomination of the head- 

 master, in July next. ThL- candidate so nominated will be 

 required to pass the Entrance Examination of the Institution, to 

 be held in the following October. It is the intention of the 

 Committee of the Institute to offer this Scholarship annually 

 for six years, beginning with 1886. The object of the Central 

 Institution is to provide advanced instruction in those kinds of 

 knowledge which bear upon the different branches of industry, 

 whether manufactures or arts. 



It is intended that a subdivision of the Military and Engin- 

 eering Department of Clifton College shall have its studies 

 specially, though not exclusively, directed with a view to 

 prepare for entrance to the Central Institution and similar 

 Engineering and Technical Colleges. 



SOCIETIES AND ACADEMIES 

 London 



Royal Society, February 4. — " On the Polarisation of Light 

 liy Reflection from the Surface of a Crystal of Iceland Spar." By 

 Sir John Conroy, Bart., M.A. of Keble College, Oxford. Com- 

 municated by Prof. G. G. Stokes, P.R.S. 



In the year 1819 Sir David Brewster communicated to the 

 Royal Society {Phil. Trans., 1819, p. 145) an account of some 

 experiments he had made on the polarisation of light by reflec- 

 tion from ihe surface of double-refracting substances, and 

 showed that Malus's statement with regard to Iceland spar was 

 incorrect. 



Malus said that Iceland spar behaves towards the light it 

 reflects like a common transparent body, and that its polarising 

 angle is about 56° 30', and that, whatever be the angle compre- 

 hended between the plane of incidence and the principal section 

 of the crystal, the ray reflected by the first surface is always 

 polarised in the same manner ("Theoriede ia Double Refrac- 

 tion," pp. 240, 241). 



Some years later Seebeck made a number of very accurate 

 observations on the same subject, and in 1835 and 1837 Neu- 

 mann published an account of further experiments that he had 

 made on the reflection of light by Iceland spar. 



He begins his second paper by a brief summary of the results 

 obtained by Brewster and Seebeck. " Brewster found that the 

 angle of complete polarisation for calc-spar depends on the posi- 

 tion of the reflecting surface relatively to the axis, and upon the 

 position of its principal section to the plane of reflection ; he 

 also found that when the reflecting surface is covered with a 

 liquid the plane of polarisation of the completely polarised ray 

 does not coincide with the plane of reflection, but makes a 

 smaller or greater angle with this ; when a cleavage-face of calc- 

 spar is covered with oil of cassia this deviation may amount to 

 go°. The knowledge of these phenomena has only been further 

 advanced in recent times. Dr. Seebeck has so followed out, by 

 means of most accurate determinations, the influence of optically 

 uniaxial crystals upon complete polarisation that the angle of 

 incidence at which this occurs can be determined as accurately 

 beforehand as it can by Brewster's law in the case of uncrystal- 

 lised bodies. Seebeck also discovered that the deviation of the 

 plane of polarisation from the pl.ane of reflection, which 

 Brewster had observed, also occurs when the ray of light falls 

 directly from air on to the surface of the crystal." 



Seebeck's observations having been mainly directed to the 

 determination of the angle of polarisation, Neumann's object 

 was to determine the azimuth of the plane of polarisation of the 

 reflected light. 



Seebeck and Neumann only repeated a portion of Brewster's 

 experiments, and no one except Sir David Brewster appears 

 to have made any determinations of the angles and azimuths of 

 polarisation when the spar was in contact with media other than 

 air. 



Prof. Stokes very kindly called my attention to these experi- 

 ments of Sir David Brewster, and pointed out that, as they had 

 never been published in detail, and had not been repeated by any 

 one else, it was desirable that further observations should be 

 made on this subject. The experiments, the results of which I 

 have the honour of submitting to the Royal Society, were under- 

 taken at Prof. Stokes's suggestion, and in carrying them out I 

 had the beneiit of his advice. 



The apparatus used was essentially the same as that employed 

 by Seebeck ; the divided circle of the goniometer was, however, 

 horizontal, and not vertical, as in Seebeck's instrument, and the 

 arrangement for keeping the reflected ray constantly in il e axis 

 of the observing-tube, whilst the angle of incidence was varied, 

 differed from that employed by him. 



The measurements were made by altering the angle of in- 

 cidence and the azimuth of the observing Nicol until the light 

 reflected by the Iceland .spar was reduced to a minimum, the 

 position of the crystal remaining fixed. 



In order to obtain anything like accurate results with observa- 

 tions of this kind it is necessary to make a large number of 

 determinations and take their mean : it was obvious that there 

 were two ways in which any given number of observations 

 might be grouped, either by making a good many separate 

 determinations for a few positions of the crystal, or by making 

 a few observations at a number of diflferent azimuths ; the latter 

 alternative being the one adopted, two readings were made at 

 seventy-two different azimuths of the crystal. 



Two complete series of observations were made with cleavage- 



