364 On the Crystalline Forms of Artificial Salts. [May, 



Prop. IX. (Fig. 11.) 



If E e be the side of an equilateral triangle inscribed in the 

 circle whose centre is c, and A b any chord intersecting it per- 

 pendicularly in o ; assuming o a equal to A o, and drawing the 

 radius c a z, I say that the angle at the periphery A £ e is the 

 third part of the angle at the centre a c z. 



Draw e r perpendicular to E e, and therefore equal to radius. 

 Then a b — e r [for drawing r s perpendicular to A b, it is plain 

 that a b = o s = e r]. Since therefore the three lines e r, a b, 

 c D are equal and parallel, the lines e c and r D, a c and b D are 



\ r e 



parallel. .*. angle e cz — r~D b = AEe = — — . .'. e c z, or 



AEe, = ^f-. Q.E. D. 



I here dismiss the subject for the present, probably for ever ; 

 yet not without a hope that some other qualified person may be 

 induced to pursue the train of investigation, which I have 

 pointed out. I have hazarded the expression of my opinion, 

 that it will yet lead to the trisection of an arc by plane geome- 

 try. I even suspect that I see how the trisection of the arc 

 A ed (fig. 10) may be derived from the trisection of the arc Aba. 

 But I must resign it into other hands. 



Article VIII. 



On the Crystalline Forms of Artificial Salts. 

 By H.J. Brooke, Esq. FRS. 



(Continued from p. 288.) 



Per chloride of Carbon. 



I am indebted for these crystals to Mr. Faraday. Their 

 planes, although very brilliant while inclosed in the bottle on 

 whose sides they have been deposited, soon become dull on 

 exposure to the air. I have not found them 

 cleavable in any direction, but a right rhom- 

 bic prism may be regarded as their primary 

 form. 



P on M, or M'. 



P on c 



P on h 



c on h 



« • • . 



90° 

 119 



90 

 150 



M on M' 122 



Mon/i 119 



0' 



40 





 20 











Miniate of Cobalt. 

 These crystals, which I have received from Mr. Cooper, may 



