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clove-brown, and they are more transparent than the orange-red 

 octohedrons. One of these is an obHque rhombic prism, the solid 

 lateral angles replaced. Another is probably a right rhombic 

 prism. All these crystals, however, are very minute, and have, 

 on this account, hitherto baffled his attempts at measurement of 

 the angles. But under a powerful microscope all the planes are 

 distinctly and clearly visible. Rose, in his admirable papers on 

 titanic acid, observes that Rutile, Anatase and Brookite, all oxides 

 of titanium, but of incompatible crystalline forms, make the first 

 clear instance of trimorphism, so that the variety of forms ob- 

 served are not extraordinary ; nay, further investigation will pro- 

 bably prove that the oxide of titanium may, in its crystalline 

 form, be polymorphous. 



Mr. T. thought it proper to notice that Monticelli and Covelli, 

 in their Prodromus of the Mineralogy of Vesuvius, describe a 

 siliceo-calcareous titanite or sphene, in the form of the octohedron 

 with a rhombic base, measuring 103.20 to 131.16. This he had 

 not seen ; nor did they analyze it. 



Prof. H. D. Rogers submitted some verbal remarks on 

 the occurrence of crystals of fluate of lime in Cannel coal. 



Prof. Rogers stated that his attention had been recently drawn 

 to the frequent violent snapping of the English Cannel coal, 

 which he had been using in his grate, and to the almost explosive 

 dispersion of small fragments of fluor spar, about the apartment, 

 which accompanied the louder crepitations. He had satisfied 

 himself, by watching the phenomenon, that the fluor spar was 

 derived from the body of the coal, since it was thus projected 

 from the grate when nothing had been placed upon the fire but 

 large and clear lumps of the coal, and afterwards he had de- 

 tected a small isolated crystal of the mineral upon breaking a 

 piece of the coal. Some of the fragments of the fluor scattered 

 into the room were more than half an inch in diameter, and 

 retained portions of the original crystalline faces, indicating that 

 it is probably lodged, within the coal, in insulated crystals. He 

 mentioned this as the first instance, within his knowledge, of the 

 discovery of any of the compounds of fluorine in a substance ap- 

 pertaining to the vegetable kingdom ; and he intimated that, 

 since this element exists, as is now admitted, in the bodies of 



