1879.] 



President's Address. 



4^9 



turned to the President for his Address, and that he be requested to 

 allow it to be printed." 



The President then proceeded to the presentation of the Medals : — 



The Copley Medal has been awarded to Rudolph Julius Emmanuel 

 Clausius, Foreign Member of the Royal Society, for his investigations 

 in the Mechanical Theory of Heat. 



The Mechanical Theory of Heat as at present understood and taught 

 has been so essentially a matter of growth, that it would be difficult to 

 assign to each investigator the precise part which he has taken in its 

 establishment. It will, however, be admitted by all, that the re- 

 searches of Clausius rank high among those which have mainly con- 

 tributed to its development. These researches extend over a period 

 of thirty years, and embrace important applications of the theory not 

 only to the steam engine, but to the sciences of electricity and 

 magnetism. 



Even to enumerate those who have contributed to one branch of the 

 subject, viz., the Kinetic Theory of Grases, would be beyond my pre- 

 sent purpose and powers ; but as Clausius himself states, both Daniel 

 and John Bernoulli* wrote on the subject. And, even, to go back to 

 earlier times, Lucretiusf threw out the idea ; while Grassendi, and oar 

 own Boyle, appear to have entertained it. Within our own recollection. 

 Joule, Meyer, Kroning, Clerk Maxwell, and others have made in- 

 valuable contributions to this branch, as well as to the general subject 

 of the Mechanical Theory of Heat. But however great the value of 

 these contributions, it may safely be stated that the name of Clausius 

 will always be associated with the development of earlier ideas into a 

 real scientific theory. 



The Davy Medal has been awarded to P. E. Lecoq de Boisbaudran. 

 The discovery of the metal gallium is remarkable for having filled a 

 gap which had been previously pointed out in the series of known 

 elements. Mendel ejeff had already shown that a metal might probably 

 exist, intermediate in its properties between aluminium and indium, 

 before Boisbaudran's laborious spectroscopic and chemical investi- 

 gation of numerous varieties of blende led him to the discovery and 

 isolation of such a metal. 



The separation of the minute traces of gallium compounds from 

 blende is an operation presenting unusual difficulty, owing to the cir- 

 cumstance that compounds of gallium are carried down by various 

 precipitates from solutions which are incapable by themselves of 

 depositing those compounds. 



# In the lOtli section of his " Hydrodynamics." 

 f " De rerum Natural," lib. ii, 111—140. 



