1879.] natural sciences of philadelphia. 195 



July 15. 

 The President, Dr. Ruschenberger, in the chair. 

 Fourteen persons present. 

 The death of J. B. McCreary, a member, was announced. 



July 22. 

 Dr. Joseph Leidy in the chair. 

 Sixteen persons present. 



Explosion of a Diamond. Prof. Leidy exhibited a black agate 

 sleeve button, having mounted upon it, centrally in a raised gold 

 band, a rose diamond about 7 mm. broad. It had been submitted 

 to him by Mr. Ernst Kretzmar, jeweller, who informed him that 

 the person who wore it recently was leaning with his head upon 

 his hand, on a window ledge in the sun, when the diamond ex- 

 ploded audibly, and with sufficient force to drive a fragment into 

 his hand, and another into his forehead. On examining the dia- 

 mond, the fractured surface, following a cleavage plane, exhibits 

 apparently the remains of a thin cavity, such as is sometimes seen 

 in quartz crj'stals. The fracture also exposes a conspicuous par- 

 ticle of coal. Prof. Leid} T thought that the explosion had been 

 due to the sudden expansion of a volatile liquid contained in the 

 cavit} 7 , as frequently occurs in cavities in many minerals. 



Mr. Goldsmith thought that the liquid might be carbonic acid, 

 as he was impressed with the idea that diamonds originated from 

 this material in the liquid condition. 



July 29. 



The President, Dr. Ruschenberger, in the chair. 



Twenty-four persons present. 



The deaths of Francis Garden Smyth, M.D., a member, and 

 Prof. Edouard Spach, a correspondent, were announced. 



Remarks on Orgyia Prof. Leidy remarked that Orgyialeucos- 

 tigma, which now seriously infested the shade trees of our city, 

 especially the horse-chestnuts and silver-maples, had recently 

 passed into the moth stage. The trunks of the trees, and the 

 surrounding railing of the square opposite to the Academy ex- 



