480 On Stokesite — a New Mineral from Cornwall. 



It was not possible to make the experiment at a very low 

 pressure, the number of cells at my disposal being insufficient 

 to produce discharge under such circumstances. When the 

 pressure is not very low a beam of cathode rays, originally 



Fig. l. 



sharp, becomes diffuse after it lias gone a short distance, doubt- 

 less owing to the collision of the particles constituting the 

 cathode stream with the surrounding gaseous particles. The 

 deflected beam in my experiments had not quite so long a 

 distance to go as the undefiected one before striking the glass. 

 This I am inclined to think is the explanation of the extra 

 sharpness of the deflected patch when the battery was used. 



It is to be concluded then that the formation of the mag- 

 netic spectrum is due to a peculiarity of the induction-coil. 

 The cathode rays produced by a battery are homogeneous. 



LII. On Stokesite — a New Mineral from Cornwall. By A. 

 Hutchinson, M.A., Fellow of Pembroke College, Cam- 

 bridge *. 

 AMONG the specimens in the Came collection, recently 

 acquired for the Cambridge Mineralogical Museum, 

 has been found a crystal whose characters prove it to belong- 

 to a new mineral species. This mineral I propose to call 

 Stokesite in honour of Sir George Gabriel Stokes, Bart., 

 whose jubilee as Lucasian Professor was this year celebrated 

 by the University, and whose researches in Physical Optics 

 have proved so valuable to mineralogists. 



The specimen consisted of a single, colourless, transparent 

 crystal about 10 millimetres long. Its crystallographic and 

 optical characters are as follows: — 

 System : Prismatic. 



a: b: c=0-3479 : 1 : 08117. 

 Forms present : b {0 1 Oj- and v {1 2.1}. 

 The crystal cleaves with ease parallel to the face 010, and 

 * Communicated by the Author. 



