A. M. Mayer—Researches in Electro-Magnetism. 205 
_— the core in the line of the dipping- needle this small 
esidual | magnetism could be reduced to 10’ or 15’ deflection, 
thus produced. The core was now handled very carefully to 
prevent all hieelidcnas or blows, and placed in an E. and W. 
horizontal lin 
The tube was 18 placed i in helix E and the current passed.. It 
was then very slowly and steadily withdrawn, so as radually to 
let down its magnetism, the tube removed several fet from the 
helix and the current broken. This operation was repeated 
until the tube had attained as high a degree of magnetization as 
could be given to it with the same constant current in the he- 
es and a further repetition of the process caused no increased 
deflection in the needle. The tube was then carefully ene 
in an E. an orizontal line and the core slowly introduced 
and so that the 8. pole of the core was in the S. end of the tube. 
It is important in all these manipulations to keep the core and 
tube in a horizontal plane, for if they are inclined to the horizon, 
during the experiment, the magnetic condition is changed and 
the operations have to begin anew. The degree of susceptibil- 
ity of very soft iron to a change of inclination can only be ap- 
preciated by those who make the trial. 
The tube with enclosed wire-core was now introduced into 
the helix and the current passed; then withdrawn, and this re- 
peated (as in the above process on tubes alone), until the needle- 
deflection showed no increase of magnetic force. This deflec 
tion was then compared with that previously produced by the 
tube cane! alone. 
the interior electric currents really flow as Ampére’s 
ianes. states, then when the core is in the tube and the maxi- 
mum magnetization reached, the combined effect of tube and 
enclosed core on the needle should be less that given by the 
tube alone without the central core; for, in the former case the 
of core is N and will therefore neutralize a portion of the tube’s 
pie on the needle. Now this was found to be invariably the 
in all the experiments made; and how can it otherwise be 
expiant It is known that the combined force of two mag- 
nets with like poles placed oe is less than the sum of the 
forces of the separate bars separately measured; but the force 
of the two together is always greater than that of one alone. 
But we here have a tube and enclosed insulated core with like 
poles together giving, after magnetization (in the same conditions 
exactly as that given to the tube alone) a less effect than that 
given by the tube alone. Therefore these facts show, to my 
