242 Contributions to Electricity and Magnetism. 
The wire conducting the secondary current is represented by 8, that 
conducting the tertiary by c, and the other wire, to receive the 
induction from these, by d. The 
direction of the influence, as be- 
fore, is indicated by + 0 — — 
é&c., and the third wire is again 
seen to be in the plus region of 
the one current, and in the mi- 9 
mus of the other. If, however, 
d is placed sufficiently near ec, 
then neutralization will 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. 19, 
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 direc- 
tion 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 eléctricity, 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. 
this class are the discoveries of Savary, on the alternate magnet 
ism of steel needles, placed at different distances from the line of 
a discharge of ordinary electricity,* and also the magnetic, scree? 
ing influence of all metals, discovered by Dr. Snow Harris of 
Plymouth.+ A comparative study of the phenomena observe 
by these distinguished savants, and those given in this pape 
would probably lead to some new and important developments. 
Indeed every part of the subject of electro-dynamic induction 
appears to open a field for discovery, which experimental industry 
cannot fail to cultivate with immediate success. 
Fig. 16. 
11 flo+ 
11 
+++]ro] 
* Annales de Chimie et de Physique, 1827. 
