PHYSICS. 219 



ond and concluding portion of his paper on the diffusion of va- 

 pors through earthenware cells. His apparatus consisted of a 

 graduated tube of glass, having a porous earthenware cell at 

 top, the upper portion of the apparatus being placed within 

 a bell-jar into which the vapor could be conducted. A soap 

 film placed half-way in the tube indicated the direction of 

 diffusion as well as its amount by the direction and extent 

 of its motion. With, this apparatus the vapors of water, 

 chloroform, alcohol, and ether were experimented with. The 

 author concludes from his results that vapors follow the 

 same law of diffusion as that discovered by Graham for 

 gases, i. c, that the times of diffusion are directly and the 

 velocities of diffusion are inversely proportional to the square 

 root of the density of these vapors. 



Daubree has experimented upon the mechanical actions of 

 incandescent gases. A plate of steel twenty-three square 

 centimeters in area, and weighing 3.479 grams, was placed 

 in a powder-chamber of forty-three cubic centimeters capac- 

 ity, in which twelve grams of powder were exploded by an 

 electric spark. The plate of steel was found completely 

 fused into a strangely twisted and puffed-out mass. An im- 

 palpable powder of ferrous sulphide was found in the cham- 

 ber, and the plate had lost 0.738 gram in weight. In other 

 experiments in which a minute opening existed between the 

 powder-chamber and the air, closed by a steel conical plug, 

 he found that when the plug was not completely screwed up, 

 gases escaped at the instant of explosion, which completely 

 melted away the conical part of the plug, and excavated deep 

 furrows in the cylindrical portion. The author applies these 

 facts to the solution of some geological problems. 



ACOUSTICS. 



Lord Rayleigh, in a lecture delivered before the Royal In- 

 stitution, has discussed the theory of maintained vibrations 

 in Acoustics, confining himself to that class of such vibra- 

 tions of which heat is the motive power, and particularly to 

 the case.w 7 here the vibrating body is a mass of air more or 

 less completely confined. The most common form of the 

 phenomenon is that often observed in blowing a bulb on a 

 glass tube, first investigated by Sondhauss, though the more 



