106 A, M, Mayer—Researches in Electro-Magnetism. 
mind, that the deduction from Ampére’s theory is verified by 
experiment; and that we have succeeded in giving to a core in 
the interior of a tube a polarity the reverse of that given to the 
tube itse 
We here present the following experiments, which are typical 
of all made; the others only differing in quantity with a change 
of distance from the needle and a change in the intensity of the 
current in the helix. 
The marked ends of tubes were S. poles, and 8. 10° E. 
means that when tube or core or both were placed W. of the 
center of the compass-needle that the 8. end of needle was de- 
flected 10° E. If the same end is deflected W. then the marked 
end is a N. pole. 
Ex. 24. Be sents with tube of 1:03 in. diam. is given 
under column A; those with tube of 1°31 in. diam. under col- 
umn B. Tangent galvanometer in all the experiments was at 
80°. Tube and core placed 74 inches W. of needle. 
Marked end of tube placed in §S. pole of helix and A B 
withdrawn (as descibed above). Repeated 6 times S.17°18’E. §. 21° ie E. 
OU 86 sho eg 4 
Introduced tube again and withdrew 
ob co sb “ Oe ence fad ats ee chy aH tt “91 40 ‘ 
Care yincet WF. Oe meee eo a oo Eee eee 
Core slowly and steadily introduced into tube so that 
; core was in 8. end of tube; then tube and 
core introduced into helix EH. and withdrawn 6 
times wig 9 ee a 
Introduced and withdrew tube and core again_.--- 18-198 S99 18 
+h “ “ib 3 “ +6 Obs it a “16 16° (og ps oo 
‘ 3 “ “ “ “ Ceres eis ++ 99. 18. 4 
While tube remained in position W. of compass the 
core was slowly withdrawn from the tube. Tube 
now alone deflected......... is ee ee ae ae 
Core now alone deflected 26.50 M2 -10W. 
with enclosed cores acted together on the needle after having 
been magnetized in exactly the same circumstances; also, that 
when the tubes, remaining undisturbed in their position, W. of 
the needle, had the cores withdrawn, the needle was deflected 
1° 25’ more in Exp. A and 1° 20’ more in Exp. B than when the 
tubes with enclosed cores both acted upon the needle. : 
In the break-circuit experiments the effects are more compli- 
cated by reason of the instantaneous and intense extra-current 
in the helix which causes a sudden inductive action on the tube 
