ADDRESS OF PROF. A. M. MAYER. 495 



through many convolutions of high resistance. He shows that plates 

 of metal, when their surfaces arc continuous, screen the inductive 

 action of a current of one order cm the succeeding order, but that 

 when a sector is cut out of the metal plate the screening effect dis- 

 appears. The same phenomena of induced currents of different 

 orders he tracks through the inductive actions of the discharge of 

 the Leyden jar and of the ordinary frictional electrical machine in 

 the most skillful manner, and shows in what these phenomena differ 

 from those produced by the inductive actions of the discharges of 

 the voltaic battery. 



In the time allotted us it is impossible to give even the most con- 

 cise abstract of these beautiful investigations. They are however 

 known to vou all. They form part of the doctrine of modern physics. 

 These researches into the nature and laws of the induced currents 

 of different orders are the most finished of Henry's works and will 

 ever be regarded as models of careful and thorough scientific work. 



We here leave Henry's researches in electricity with the regret 

 that we have been able only to give but meagre and imperfect 

 accounts of them; and that the occasion does not permit me to 

 mention even by their titles several of his investigations in this 

 department of knowledge. 



Henry bad a versatile mind, and did not confine his attention to 

 the study of electricity. His genius has adorned all departments 

 of' Physics. His researches in molecular physics, though not exten- 

 sive, are remarkable. Here his fertile suggestions and original 

 methods of research have instigated others to follow out the paths 

 which he has pointed out. 



In 1839 Henry made a very curious discovery as to the permea- 

 bility of lead to mercury. So permeable indeed is this metal to the 

 fluid that he found mercury would ascend a lead wire to the height of 

 a vard in a few days. He even made what might be called, so fat- 

 as their tonus are concerned, syphons of lead which would nearly 

 empty a vessel of mercury by gradually drawing the fluid over its 

 sides. Subsequently, in 18-15, with the assistance of Mr. Cornelius, 

 of Philadelphia, he succeeded in showing that copper when heated 

 to the melting point of silver would absorb the latter metal. This 

 he distinctly proved by subsequently dissolving off the surface of 



