244 M. Werner Siemens on the 
magnetic resistance of iron varies with the strength of its 
magnetization. 
As is known, and as we may also see from the above expe- 
riments, the magnetism in a closed electromagnet increases 
at first more rapidly than the current-strength. The increase 
of magnetism then soon attains a maximum, and with further 
increase of current-strength sinks slowly down to a very 
small amount. In this behaviour of magnetic substances the 
initial increasing action of the magnetizing force to a maximum 
is very striking. The position of this maximum is dependent 
upon the properties of the iron. With softiron the maximum 
is sooner attained with equal magnetizing force than with 
harder iron. It is therefore not improbable that this initial 
feebler action of the magnetizing force is always only a con- 
sequence of the imperfect softness of the iron. In order to 
examine this more closely I had two similar rings made, the 
one of the softest iron rod possible, the other of soft steel. 
The external diameter was 50 millim. and the internal dia- 
meter 35 millim.; and they were similarly wound each with 
two coils, the lower one of 350 turns of wire 0-2 millim. thick, 
the upper one of 190 turns of wire 0°75 millim. thick. The 
second coil served for the magnetizing current, the first as 
induction-coil. The first column of Table III. gives the 
current-strengths as measured ; the second the corresponding 
magnetic moments of the iron ring as measured by the de- 
flection of the reflecting-galvanometer; the third the increase 
in magnetism for an increase in current-strength of 0-001 
ampere calculated from these numbers; the fourth and fifth 
columns give the same values for the steel ring. 
TABLE III, 
Iron.| Iron. | Steel.| Steel. Iron.| Iron. | Steel. | Steel. 
Ourrent- Increase Increase |; Current- Increase Increase 
strength.|Deflec | for zo'55|Deflec-| for yo'gq/| strength | Deflec-| for z¢55 |Deflec-| for ;355 
tion, | ampere. | tion. | ampere. tion. | ampere. | tion. | ampere. 
0:001 3:2 3°2 35 35 0-100 | 1810} 65 430 5:0 
0-002 7 3°25 GZ, 37 0:15 4520} 54 760 6°6 
0:004 15 4 15 34 0-2 6880} 47:2 1120 72 
0:008 36 5:2 29 3°5 0:25 8640] 35:2 1640} 10:4 
0-01 46 5 35 30 0-3 9900} 25:2 2500| 17-2 
0:02 114 68 wi a7 0-4 11500! 16 4950| 24:5 
0:03 196 81 112 4:0 05 12400 9 7000} 380°5 
0:04 300 10°5 155 4°3 06 13150 75 8750} 17:5 
0:05 410 tel 195 4:0 0-7 13750 6 10000; 12°5 
0:06 550 14 245 5:0 08 14250 5 11000} 10:0 
0:07 710 16 290 4:5 0:9 14600 3°5 | 11900 9°0 
0:08 895 18°5 340 5:0 1:00 =| 15000 4 12550 6:5 
0:085 {1015 24 360 4-0 iil 15250 2°5 | 13150 6:0 
0:090 |1160 29 380 4-0 1:2 15500 2°5 | 18600 4:5 
0-095 aut at 405 5:0 15 16150 2-1 15000 4:6 
