278 



Anniversary Meeting, 



[Nov. 30, 



the instruction derived from them of comparatively little value. The pro- 

 duction of an apparatus by which the actual strain experienced in successive 

 parts of the bore may be recorded, is in fact the first step in a scientific 

 inquiry which should establish the proper relations between the form of 

 the cartridge and the gun. But for the production of an efiicient appara- 

 tus for this purpose, a chronoscope of greater delicacy and perfection than 

 any we have hitherto possessed in England is indispensable. A chrono- 

 scope recently devised by Captain Schultz of the French Artillery appears, as 

 far as can be judged previous to a practical trial, to correspond to these 

 conditions, and to be likely to supply a means of surmounting the difficulty ; 

 it is not improbable that it will be tried in the present year. 



I proceed to the award of the Medals. 



The Copley Medal has been awarded to Professor Julius Pliicker, Foreign 

 Member of the Royal Scciet}'-, for his researches in Analytical Geometry, 

 Magnetism, and Spectral Analysis. 



To an audience not exclusively mathematical it is obviously impossible 

 to enter into details of researches which deal with geometrical questions of 

 no ordinary difficulty. Amongst these, however, may be indicated, as 

 especially appreciated by those who are interested in the progress of ana- 

 h'tical geometry, his theory of the singularities of plane curves as developed 

 in tlie " Algebraische Curven/' with its six equations connecting them 

 with the order of the curves : the papers on point and line coordinates and 

 on the general use of symbols, may also be noticed as establishing his claim 

 to a position in the department of abstract science which is attained by 

 few even of those who give to it their undivided attention. But Professor 

 Pliicker has high merits in two other widely different fields of research, 

 viz. in Magnetism and Spectrology : and to these I may more freely invite 

 your attention. 



Shortly after Faraday's discovery of the sensibility of bodies generally to 

 the action of a magnet and of diamagnetism. Professor Pliicker, in re- 

 peating some of Faraday's experiments, was led to the discovery of magne- 

 crystallic action, — that is, that a crystallized body behaves differently in the 

 magnetic field according to the orientation of certain directions in the 

 crystal. The crystals first examined were optically uniaxal, and it was 

 found that the optic axis was driven into the equatorial position ; (that is, of 

 course, assuming that the magnecrystallic action is not masked, in conse- 

 quence of the external form of the body, by the paramagnetic or diamag- 

 netic character of the substance). New facts, discovered both by Faraday 

 and by Pliicker himself, led him to a modification of this law, to the effect 

 that the optic axis was impelled, according to the nature of the crystal, 

 eithe?' into the equatorial or the axial position. This subject was after- 

 wards followed out by Professor Pliicker into the more complicated cases 

 in which the conditions of crystalline symmetry are such as to leave the 

 crystal optically biaxal ; and after having recognized the insufficiency of a 



