PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 6G5 



the possibilitj^ that masses of melted matter may be distributed 

 through this crust, and give still cause to volcanic eruptions, when 

 reached by water, penetrating through the fissures in the ground. 

 The extent over which an earthquake is felt, depends on the 

 depth where it originates; at a small depth it will only ])e felt 

 over a small surface; but an earthquake as that which destroyed 

 Lisbon in 1755, and was felt after the computation of Hurabolt 

 over a surface four times greater than Europe; from the Alps to 

 Sweden, Canada, the West Indies, the north of Africa; and on the 

 whole northern Atlantic ocean the shocks were felt by vessels. 

 This suggests an origin of great depth, and thus a crust of several 

 hundred miles in thickness. 



' Another calculation lately made as to the thickness of the earth's 

 crust, is based on an estimation of the w^eight of the Himalaya 

 mountains, a rai^ge the most extensive and highest in the world, 

 which it has been proved could not be supported by a crust of 

 only a few miles in thickness, without depressing it, and* raisino- 

 the bed of the Indian ocean; it has been calculated that it requires 

 a crust of some 400 miles in thickness to support this enormous 

 weight alone. 

 Adjourned. 



American Institute, Polytechnic Association, ) 



January 10, 18 67. \ 



Prcf. S. D. Tillman, Chairman; T. D. Stetson, Esq., Secretary. 

 The chairman opened the proceedings by the presentation of 

 the following scientific summary: 



Corundum. 

 Dr. C. T. Jackson lately found a perfect crystal of blue corun- 

 dum or sapphire (pure alemit) in the new emery mine at Chester, 

 Mass. Its form is that of a double pyramid with six planes. 

 This, with other specimens from that mine, wnll be sent by the 

 Emery Company to the Paris Exposition. 



New Artificial Solid. 

 Gypsum, if mixed with a certain quantity of water and soaked 

 in a bath of hot pitch, parts w'ith its water, and, absorbing pitch 

 in corresponding quantity, forms a substance so hard that it will 

 receive a polish and can be used in the manufacture of useful and 

 ornamental articles. 



