162 POPULAR LECTURES AND ADDRESSES. 



electric measurement in every scientific laboratory 

 in the world, and initiating a train of investigation 

 which now sends up branches into the loftiest 

 regions and subtlest ether of natural philosophy. 

 Long may the British Association continue a bond 

 of union, and a medium for the interchange of good 

 offices between science and the world ! 



The greatest achievement yet made in molecular 

 theory of the properties of matter is the Kinetic 

 theory of Gases, shadowed forth by Lucretius, 

 definitely stated by Daniel Bernoulli, largely 

 developed by Herapath, made a reality by Joule, 

 and worked out to its present advanced state by 

 Glausius and Maxwell. Joule, from his dynamical 

 equivalent of heat, and his experiments upon the 

 heat produced by the condensation of gas, was able 

 to estimate the average velocity of the ultimate 

 molecules or atoms composing it. His estimate 

 for hydrogen was 6225 feet per second at tempera- 

 ture 60 Fahr., and 6055 feet per second at the 

 freezing-point. Clausius took fully into account the 

 impacts of molecules on one another, and the 

 kinetic energy of relative motions of the matter 



