11)0 Intelligence and Miscellaneous Articles. 



decomposes the peroxide of hydrogen into water and oxygen, precisely 

 as sulphuric acid decomposes alcohol into ether and water. But in 

 this case the colour of the solution gives actual evidence of the 

 presence of the intermediate compound by the agency of which 

 the catalytic action is effected, and which is formed, but disappears 

 from the final result. 



LXVI. Intelligence and Miscellaneous Articles. 



ON THE VELOCITY OF THE PROPAGATION OF SOUND IN GASEOUS 

 BODTES. BY J. STEFAN. 



IT appears not to have been noticed that the new theory of gases 

 admits of the application of Newton's formula for the velocity 

 of sound, if a regular arrangement of the molecules be assumed, such 

 as Kronig has employed in his important work on the theory of 

 heat. 



Let us suppose an infinitely extended space filled with a gas to be 

 divided by parallel planes into very thin layers. When condensation 

 takes place in one layer, it will pass on from layer to layer with a 

 velocity w T hich is the velocity of the propagation of sound. The new 

 theory of gases, according to which the molecules are in very rapid 

 progressive motion and behave like elastic balls when they strike one 

 another, requires that the velocity of the progression of sound should 

 be dependent upon the velocity of the progressive motion of the 

 molecules. These two velocities would be exactly equal if the 

 movements of the molecules were all in the direction in which the 

 propagation of sound took place. 



Following Kronig, let us divide the whole space filled with gas 

 into equal cubes, all of them placed in the same direction. Let us 

 suppose in each of these cubes three molecules, each one moving 

 perpendicularly between two opposite sides of the cube. Let us 

 assume that each molecule only strikes against molecules which are 

 moving in the same line and which are situated in the neighbouring 

 cubes. These hypotheses relative to the constitution of gases are 

 sufficient, as Kronig has shown, to explain the most important pro- 

 perties of gases. But in order to make the explanation simple and 

 natural, it is necessary in each particular case to represent the divi- 

 sion of the space into elementary cubes in a definite manner. If we, 

 for example, in the case before us, arrange the cubes so that their 

 two opposite sides lie parallel with the surfaces of the layers into 

 which we have divided our gas, it follows that only one third of the 

 molecules take part in the transmission of vis viva from layer to layer, 

 the third, namely, which is composed of those molecules moving 

 perpendicularly to the surfaces of the layers. In order that all the 

 molecules may play the same part in this transmission, it is necessary 

 so to place the elementary cubes that the diagonal drawn through two 

 opposite angles of the cube shall be perpendicular to the surfaces of 

 the layers. The velocity with which the vis viva or the condensation 



