Polytechnic Association Froceedinos. 779 



The length of a wave whose period is i is 



the period 



. /2VI . j~R 



and the velocity of propagation of such a wave 

 I St 



t 2n V 2Tr 



The motion of the wire pendulum represents the motion of the 

 mast of a raft floating on the wave's surface; the upper portion of 

 each upright wire shows the motion of a long, thin body floating 

 in a vertical position, as a board end down; the varying inclination 

 of the two bodies, or wires, to each other shows the kind of strain 

 produced by wave-action on a floatiug body, both broad and deep, 

 such as the hull of a vessel. 



In shoal water the orbits are no longer circles, but ellipses or 

 ovals, with the eccentricity increasing as the depth diminishes, while 

 the front slope of the wave becomes increasingly steeper than the 

 back, until the crest finally curls over and breaks in surf. 



The apparatus has been jjatented, and is manufactured by Messrs. 

 E. S. Ritchie & Son, of Boston, Mass. Adjourned. 



December 19, 1867. 



Prof. S. D. Tillman in the chair. 



The Chairman opened the proceedings by reading the following 

 scientific notes: 



SUPPLY OF GOLD AND SILVER. 



In the year 1865, the principal sources of supply throughout the 

 world yielded 559,587 troy pounds of gold, and upward of 400,000 

 pomids of silver. 



GRASS SPONGE. 



A vegetable growth, found in profusion on the coral reefs of the 

 coast of Florida, Mexico, and at the Bahamas, called grass sponge, 

 has been used in this country, in place of hair, for stuffing sofas, 

 chairs and beds. 



