148 Miscellaneous Intelligence. 
8. On optical figures produced by the disintegrated surfaces of 
erystals ; by Sir Davin Brewster, (Phil. Mag. [4] v, 16.)—This 
An octahedron of alum, when perfect, gives a single reflection of a 
candle from one of its surfaces. But on immersing it for an instant in 
Brewster varied the experiments in many ways, and made similar trials 
with fluor spar, carbonate of lime, ete., and developed the most won- 
derful results. 
Different solvents were found to produce different optical figures. 
Alcohol and muriatic acid act on alum differently from water. Othe 
remarkable changes were produced by immersing crystals in saturated 
solutions of salts. 
Mechanical abrasion by means of a piece of sandstone, hone or file, - 
produced ina rude manner the figures given by solution; but what 
was very remarkable, the figure had a reversed position, or was like 
what solution would produce on the opposite face. 
€ power of producing the optical figures may be transferred from 
the crystal surface to wax or isinglass; and the impressions on isinglass, 
thite or labradorite, yellowish brown olivine or garnet, and black augite- 
merican Association for the Advancement of Science.—This 
Association will hold its next annua! meeting at Cleveland, Obio, dur- 
ing the week commencing with the 28th of July. Professor Peirce 
Cambridge is the President for the yonr,: «3 
