The Viscosity of Gases and Molecular Force. 



507 



likewise depends upon the ratio between the diameter and 

 length. 



5th. That there are two maxima: one produced by increasing 

 the current, another by decreasing the current from that point 

 which produced the first maximum. 



6th. They confirm Prof. A. M. Mayer's observations, that 

 the first contact gives more expansion than the second and 

 following contacts, and, further, even these seem to disagree 

 slightly among themselves, the expansion falling off with 

 subsequent contacts. 



Fiff. 4. 



In fig. 4 I have plotted the expansion-curves of three of the 

 bars which show the greatest differences. 



Mr. Bidwell's curves are similar in form to those produced 

 by bars I. and II., while M. Alfonse Berget's curve, as would 

 be expected, agrees more closely in form with that of bar V. 



The experiments were carried on in the physical laboratory 

 of Clark University, under the direction of Prof. A. Gr. 

 Webster, to whom acknowledgment should be made for 

 frequent suggestions. 



LIT. The Viscosity of Gases and Molecular Force. 

 By William Sutherland*. 



IT is now well known that a full acceptance of the kinetic 

 theory of gases was suddenly accelerated by the experi- 

 mental verification of Maxwell's theoretical discovery of the 

 paradoxical independence of the coefficient of viscosity of a 

 gas on pressure. Contrary to the general sentiment of phy- 

 sicists, the premisses of the kinetic theory were found to lead 

 to the conclusion that a vibrating pendulum would be just as 

 much hindered by gaseous friction in an environment under 

 one twentieth of an atmo pressure as under twenty atmos, and 

 experiment soon afterwards showed the coefficient of viscosity 



* Communicated by the Author. 



