288 Mr. Levy on the Forms of Artificial Salts. 



spectively, 98° 14', and 91° 36'; and that of m on t, 96° ; the 

 lengths of the three edges,/, d, h, meeting in the point o, are 

 nearly in the ratio of the numbers 1., 0.55, 1.125. 



Cleavage. — Very easily obtained, parallelly to all the planes 

 of the primitive. 



Prussiate of Potash. 



h/ . , 



try/. 41 UxL/yy^/ 



^ ''p "Wi. 



Incidences. 



PouP 980 11' 



pi 135 40 



a« 112 10 



61 on a' 119 57 



ei 90 



Primary form. — Octahedron, with a square base, in which 

 the incidence of two adjacent faces of the upper pyramid 

 is 98° 11'. 



Cleavage. — Easy, in a direction perpendicular to the axis of 

 the octahedron. 



[To be continued.] 



Art. IX. Historical Statement respecting Electro-Mag- 

 netic Rotation. By M. Faraday, Chem. Assist, in 

 the Royal Institution. 



In the Xllth Volume of this Journal, at page 74, I published 

 a paper on some new electro-magnetical motions, and on the 

 theory of magnetism. In consequence of some discussion, 

 which arose immediately on the publication of that paper, and 

 also again within the last two months, I think it right, both in 

 justice to Dr. Wollaston and myself, to make the following 

 statement : — 



