Mr. W. J. Macquokn Rankine on the Science of Energetics. 381 



sent to the Magistrates and other municipal authorities ; and that the 

 members of the Society would be furnished with tickets for their friends. 

 Dr. Taylor, Professor of Natural Philosophy, Anderson's University, 

 read a paper " On the Nature and Causes of Hurricanes." 



April 18, 1855. — The President in the Chair. 



Pbofessoe William Thomson gave an account of " Recent Experi- 

 mental Investigations in Thermo-EIectricity." 



May 2, 1855 (the Concluding Meeting of the Session was held this even- 

 ing). — William Gourlie, Esq., Vice-President, in the Chair. 



Mb. J. Napiee read a paper " On the Chemistry of Trap Dykes in 

 Arran." 



Mr. W. J. Macquorn Eankine read a paper " On the Science of 

 Energetics." 



Outlines of the Science of Energetics. By William John Macquoun 

 Rankine, Civil Engineer, F.E.SS. London and Edinburgh, «S:c. 



I. What constitutes a Physical Theory. 



An essential distinction exists between two stages in the process of 

 advancing our knowledge of the laws of physical phenomena ; the first 

 stage consists in observing the relations of phenomena, whether of such 

 as occur in the ordinary course of nature, or of such as are artificially 

 produced in experimental investigations, and in expressing the relations 

 so observed by propositions called formal laws. The second stage con- 

 sists in reducing the formal laws of an entire class of phenomena to the 

 form of a science ; that is to say, in discovering the most simple system 

 of principles, from which all the formal laws of the class of phenomena 

 can be deduced as consequences. 



Such a system of principles, with its consequences methodically de- 

 duced, constitutes the physical theory of a class of phenomena. 



A physical theory, like an abstract science, consists of definitions and 

 axioms as first principles, and of propositions, their consequences ; but 

 with these differences : — first, That in an abstract science, a definition 

 .'issigns a name to a class of notions deiived originally from observation, 

 but not necessarily corresponding to any existing objects of real phcno- 



