450 Scientific Intelligence. 
Among the species of the Lignitic beds, thirty-two are stated 
by Lesquereux to occur also in the Arctic; and, of these Are- 
SCIENTIFIC INTELLIGENCE. 
L CHEMISTRY AND PHYSICS. 
1. On the Velocity of Sound in Gases as a means of determin: 
ing their Molecular Weights. The fundamental importance of 
molecular weight in modern chemical theory gives interest to any 
methods looking toward its more convenient or more accurate 
been determined from its vapor-density, from its diffusibility, or 
‘from its specific heat. BrnpER now proposes to use the velocity 
of sound to accomplish this result. In gases, this velocity has 
the well-known relation to their density expressed by the formula — 
v= |°*, in which ¢ represents the elasticity of the gas, $ the co- 
efficient 1°41, obtained by dividing the specific heat at constant 
pressure by the specific heat at constant volume, and 6 the density. 
For any other gas of density 6’ we should have C= —- 
whence v:v'::0': V6, or the velocities of sound in the two 
gases are inversely proportional to the square root of the densi 
ties. Now since ¢ is the same for all gases under similar condi- 
tions, and since, by Avogadro’s law, ; 
gases are proportional to their densities, it follows that the velocity 
of sound in any gas is inversely proportional to the square root of 
its molecular weight. In order to measure the velocity of sound 
in the given gas, Bender proposes to make use of the exceedingly 
ingenious method of Kundt.* <A glass tube about a meter long 
is 
the ends of the tube are hermetically sealed. If now this tube be 
grasped at its middle point and a wet cloth be drawn over it from 
* Pogg. Ann., exxxv, 337. Tyndall on Sound, 202-209 
. PP. a 
+ Mr. W. E. Geyer uses successfully precipitated silica, well dried. 
