144 WRITINGS OF JOSEPH HENRY. [1838 



not take place, but the two currents will conspire to produce 

 in it an induction in the same direction. A similar effect 

 would also be produced were the wire c, in Fig. 15, placed 

 sufficiently near the conductor b. 



133. Currents of the several orders were likewise produced 

 from the excitation of the magneto-electrical machine. The 

 same neutralizing effects were observed between these as in 

 the case of the currents from the galvanic battery, and hence 

 we may infer that also the same alternations take place in the 

 direction of the several currents. 



134. In conclusion, I may perhaps be allowed to state, that 

 the facts here presented have been deduced from a laborious 

 series of experiments, and are considered as forming some 

 addition to our knowledge of electricity, independently of 

 any theoretical considerations. They appear to be intimately 

 connected with various phenomena, which have been known 

 for some years, but which have not been referred to any 

 general law of action. Of this class are the discoveries of 

 Savary on the alternate magnetism of steel needles placed 

 at different distances from the line of a discharge of ordinary 

 electricity,* and also the magnetic, screening influence of all 

 metals, discovered by Dr. Snow Harris, of Plymouth. f A 

 comparative study of the phenomena observed by these dis- 

 tinguished savants, and those given in this paper, would 

 probably lead to some new and important developments. 

 Indeed every part of the subject of electro-dynamic induc- 

 tion appears to open a field for discovery, which experimental 

 industry cannot fail to cultivate with immediate success. 



NOTE. 



On the evening of the meeting at which my investigations 

 were presented to the Society, my friend, Dr. Bache of the 

 Girard College, gave an account of the investigations of 

 Professor Ettingshausen, of Vienna, in reference k) the im- 

 provement of the magneto-electric machine, some of the 

 results of which he had witnessed at the University of Vienna, 



* Annales de Chimie et de Physique, 1827. 

 •j- Philosophical Transactions, 1831. 



