302 WRITINGS OF JOSEPH HENRY. [1851 



other ; one of these is called the electrical fluid, and the other 

 ordinary matter. For the generalization of the same phe- 

 nomena Dufay assumed three principles, two species of elec- 

 trical, and one of ordinary matter. From either of these 

 mechanical conceptions, could be deduced all the facts then 

 known. 



It would appear however that the tendency of the present 

 day is to the accumulation of facts rather than to their critical 

 examination, or the discovery of general expressions by which 

 to represent them. Electricity and magnetism at the present 

 time consist of almost a chaos of isolated phenomena which 

 can scarcely be called scientific. Most of these however, I 

 am convinced, are capable of being referred to the theory of 

 Franklin or to that of Dufay, with the addition of a few 

 supplementary hypotheses analogous to those which we have 

 seen were added to the theory of emission. For example, we 

 shall be obliged to admit that in some cases inductive effects 

 are propagated wave-fashion; and in others, that a change 

 in the condition of the ponderable matter plays an important 

 part. Thus, as I mentioned at the last meeting of the Associa- 

 tion, I have found that in the discharge of a Leyden jar 

 through a metallic wire a series of rebounds between the 

 inside and the outside of the jar takes place precisely in the 

 same way as the equilibrium would be restored by a series 

 of waves were a quantity of air, condensed in one vessel, 

 suffered to discharge itself into another in which a vacuum 

 previously existed. I have also shown that during this dis- 

 charge a series of inductions take place, extending to a sur- 

 prising distance on all sides of the wire; and as these are the 

 results of currents in alternate directions, they must produce 

 in surrounding space a series of plus and minus motions 

 analogous to if not identical with undulations. 



Next, that a change in the condition of the matter itself is 

 required for the explanation of certain phenomena will be 

 evident from the following experiment: If portions of the 

 same current of galvanism be sent through two parallel wires, 

 or if portions of the same discharge from a Leyden jar be 

 transmitted simultaneously through two parallel strips of 



