45° 



NA TURE 



\March 1 2, i < 



a skilled geologist could produce. The President next presented 

 the Lyell Medal to Prof. H. G. Seeley, F.R.S., F.G.S., and 

 addressed him as follows : — The Council has awarded to you 

 the Lyell Medal and a grant of 40/. in recognition of your 

 investigations into the anatomy and classification of the Fossil 

 Reptilia, especially the Dinosauria. Not that you have limited 

 yourself to this field of research ; your papers on Emys and 

 Psephophorus, on Megalornis and British Fossil Cretaceous 

 Birds, on Zetiglodon, and on remains of Mammalia from Stones- 

 field, prove your extensive knowledge of vertebrate palaeon- 

 tology, as your proficiency in invertebrate is evidenced by your 

 earlier work, both stratigraphical and directly pal?eontoIogical. 

 Furthermore, your excellent edition of the first volume of 

 Phillip's "Manual of Geology" indicates an exceptional 

 familiarity with the literature of our science. Since our ac- 

 quaintance first began, some twenty years since, at Cambridge, 

 we have both had our disappointments and our successes ; you, 

 undiscouraged by the one, unelated by the other, have pushed on 

 to your present high position in science, making no enemies, 

 winning many friends. I trust that your future career may be 

 even more prosperous than your past, and that this medal may 

 be an augury of many good gifts of fortune. You will, I know, 

 believe me when I say that I feel an exceptional pleasure in 

 being commissioned to place in your hands this medal, com- 

 memorative of the great geologist whose philosophic spirit you 

 so well appreciate, and whose memory, I know, you so greatly 

 revere. The President then handed the balance of the proceeds 

 of the Lyell Geological Fund to Mr. J. J. H. Teall, F.G.S., for 

 transmission to Mr. A.J. Jukes-Browne, F.G.S., and addressed 

 him as follows : — The balance of the Lyell Donation Fund has 

 been awarded to Mr. A. J. Jukes-Browne in recognition of the 

 excellent work that he has done on the Cretaceous formation and 

 on glacial geology, and to aid him in further researches. His papers 

 on the Cambridge greensand cleared up many difncultiesconnected 

 with that interesting formation ; and in his Sedgwick prize essay 

 on the Post-tertiary deposits of Cambridgeshire he commenced 

 those investigations which have since brought us more than one 

 valuable contribution on glacial and later deposits. You can 

 tell him that his old college tutor feels a little pardonable pride 

 and much real pleasure in being the instrument of placing this 

 award in your hands for transmission to him. In presenting the 

 Bigsby Gold Medal to Prof. Renard, of Brussels, the President 

 him as follows : — When to a familiarity with geology 

 in the field and a love of nature are united the skill of a finished 

 chemist and the experience of a practised worker with the nik n 1- 

 scope, the results cannot fail to be of the utmost importance to 

 our science. These qualifications, rarely united in anv one man, 

 are in yourself combined with an untiring industry and a love of 

 science for its own sake. Thus we are indebted to you for many 

 important contributions to our knowledge in geology. Your 

 early memoir, " Surles Roches Plutoniennes de la Belgique et 

 de l'Ardenne Francaise," written in conjunction with M. de la 

 Vallee Poussin, will long be classic ; your papers on various 

 subjects connected with the Carboniferous limestone, on the 

 coticule, the phyllites, and other altered rocks of Belgium, and 

 on the deep-sea deposits, are too well known to need more than 

 mention, and in recognition of these the Council has awarded you 

 the Bigsby Medal. In placing it in your hands may I be allowed 

 to express for myself and others the hope that it will be 

 always a pleasant souvenir of your many friends on this side of 

 the Channel, some of whom, myself included, will not soon 

 forget the pleasant and, to us, most profitable days spent under 

 your guidance in geological studies by the limestone cliffs of the 

 winding Meuse and the wooded crags of the Ardennes. The 

 President then read his Anniversary Address, in which, after 

 giving obituary notices of some of the members lost by the 

 Society during the year 1884, he referred to the principal con- 

 tributions to geological knowledge which have been made during 

 the past year, both in the publications of the Society and else- 

 where in Britain, concluding with a notice of the new views 

 which have been adopted with regard to the structure of the 

 Western Highlands, and a brief history of the steps by which 

 they have been arrived at. The concluding portion of the 

 address was devoted to a discussion of the principles of nomen- 

 clature which should be followed in petrology, with remarks on 

 the classification of igneous rocks, and on the significance of 

 certain structures, especially the more minute. — Officers and 

 Council, 1885 :— President : Prof. T. G. Bonney, F.R.S. ; Vice- 

 Presidents : W. Carruthers, F.R.S. , John Evans, F.R.S., J. 

 W. Ilulke, F.R.S., J. A. Phillips, F.R.S. ; Secretaries: W. f. 



Blanford, F.R.S., Prof. J. W. Ridd, F.R.S. ; Foreign Secre- 

 tary : Warington W. Smyth, F.R.S. ; Treasurer: Prof. T. 

 Wiltshire, F.L.S. ; Council: H. Bauerman, W. T. Blanford, 

 F.R.S., Prof. T. G. Bonney, F.R.S., W. Carruthers, F.R.S., 

 Prof. W. Boyd Dawkins, F.R.S., John Evans, F.R.S., A. 

 Geikie, F.R.S., Henry Hicks, M.D., Rev. Edwin Hill, M.A., 

 (',. J. llinde, Ph.D., John Hopkinson, W. H. Hudleston, 

 F.R.S., T. W. Hulke, F.R.S., Prof. T. Rupert, F.R.S , Prof 

 J. W. Judd, F.R.S., J. E. Marr, M.A.J. A. Phillips, F.R.S., 

 Prof. T- Prestwich, F.R.S., Warington \V. Smyth, F.R.S., I 

 J. H. Teall, M.A., W. Topley, Prof. T. Wiltshire, F.L.S., 

 Rev. H. H. Winwood, M.A., Henry Woodward, F.R.S. ; 

 Assistant-Secretaiy, Librarian, and Curator: W. S. Dalla-, 

 F.L.S. ; Clerk : W. W. Leighton ; Library and Museum 

 Assistant : W. Rupert Jones. 



Physical Society, February 28.— Prof. Guthrie, President, 

 in the chair. — Messrs. G. R. Begley and O. Chadwick were 

 1 lected Members of the Society. — Mr. J. C. McConnel pre- 

 sented two notes on the use of Nicol's prism. The first note 

 related to the error in measuring a rotation of the plane of 

 polarisation due to the axis of rotation of the prism not being 

 parallel to the emergent light. After pointing out that this 

 error was, to a first approximation, eliminated by taking the 

 mean of the readings in the two opposite positions of the Nicol, 

 the author proceed to push the calculation to a second approxim- 

 ation, so as to get a measure of the residual error. This is 

 given by the equation — 



— ■ — i - \p = const. + . 24»-- sin ty cos ty, 



where 6 and 180 + 6, are the two readings of the circle : \\i the 

 angle between the plane of polarisation and a fixed plane, and 

 r the angle between the axis of rotation and the incident light. 

 This equation is practically correct for a flat-ended as well as an 

 ordinary Nicol. The residual error cannot amount to 1' in a 

 rotation of 6o° if r is less than 2°. The optical properties of 

 the Nicol tend to neutralise the geometrical error due to the 

 rotation taking place about one axis and being measured about 

 another. The second note dealt with a new method of obtain- 

 ing the zero reading of a Nicol circle. This is often defined as 

 the reading when the plane of polarisation is parallel to the 

 axis of rotation of the table of a spectrometer. A Nicol is 

 fixed on the tab'e, the light quenched by turning the Nicol 

 circle, and the reading taken. The table is then rotated 

 through 180 , the light quenched, and the reading taken 

 again. The mean of the two readings gives the result 

 required. It was described how the error due to the wan; 

 of symmetry of the Nicol might be found and eliminated. — 

 Mr. H. G. Madan exhibited and described some new forms of 

 polarising prisms. The first of these is by M. Bertram!, and 

 has been described by him (Comptes Haidus, September 29, 

 1S84). The prism consists of a parallelopiped of dense flint glass 

 of reft active index 1 '65s, the same as that of Iceland spar for the 

 ordinary ray. The glass prism is cut like the spar of a Nicol's 

 prism, a cleavage plate of spar being cemented between the two 

 halves by an organic cement of refractive power slightly greater 

 than I '65S. A beam of light traversing the prism is incident upon 

 the spar at an angle of 76° 44'. The ordinary ray passes through 

 without change, but the extraordinary ray is totally reflected at 

 the first surface. The prism gives a field of 40 . M. Bertrand's 

 prism has the great advantage of requiring only a very small 

 quantity of Iceland spar, a substance that is becoming very 

 scarce and expensive. The other prisms shown were : a similar 

 one by M. Bertrand, described in the same paper ; a double- 

 image prism by Ahrens, described in the Phil. Mag. for January. 

 1SS5 ; and a modification of the latter by Mr. Madan, described 

 in Nature for February 19. Mr. Lewis Wright pointed out as 

 a practical objection to M. Bertrand's prism that it was very 

 doubtful whether a glass could be obtained of so high a density 

 as to possess a refractive index of i"65S and at the same time be 

 colourless and unaffected by the atmosphere. He also remarked 

 that the principle of the prism was by no means new. — Prof. 

 W. E. Ayrton read a paper by himself and Prof. J. Perry on 

 " The most economical potential difference to employ with in- 

 candescent lamps." The authors commenced by pointing out the 

 importance of experiments being made on the lives of incan- 

 descentlamps, in addition toexperiments on efficiencies. Referring 

 to the experiments on life given by M. Foussat in The Electrician 

 for January 31, they showed that if / be the price of a lamp 

 in pounds, n the number of hours per year that it burns, f(v) the 



