AND STRAIN ON THE ACTION OF PHYSICAL FORCES. 
149 
Table XXX. 
M.C. 
in divisions 
of the 
scale of the 
tangent 
galvanometer 
= a. 
“ Throw ” of 
the galvanometer 
needle due to 
induction current 
by magnetization 
of the steel 
=/* *■ 
Increase of 
resistance when 
B.C. = 194° 
of tangent 
galvanometer, 
the increase 
measured 
in divisions of 
platino-iridium 
wire. 
Increase 
of 
resistance 
when 
B.C. = 29°. 
Increase 
of 
resistance 
when 
B.C. = 38°. 
Mean 
increase 
of 
resistance 
= 7- 
Increase 
of resistance 
calculated 
from formula 
p = '0386 x a 
+ '0588 x /?. 
d 
a 
V 
W 
23 
7 
1-35 
1-35 
1-30 
•31 
T93 
108 
32 
6-48 
6"48 
6-05 
•30 
•203 
152 
48 
8-83 
8-50 
8-7-5 
8-69 
8-69 
■32 
•181 
267 
82 
15-00 
15-00 
15-13 
•31 
T83 
347 
102 
18-88 
20-30 
19-00 
19-39 
19-39 
•30 
•190 
From this experiment we learn that the magnetism induced in the steel is, for the 
magnetizing forces employed, very nearly proportional to these latter, and also that the 
alteration of resistance is nearly proportional to the induced magnetism, and therefore 
to the magnetizing force. Still more closely can the alteration of resistance be cal¬ 
culated from the formula y=a.a-\-b./3, where the constants a and b, given as '0386 
and '0588, are determined from the alterations of resistance caused by values of the 
M.C. equal to 347 and 152 divisions of the scale of the tangent galvanometer. 
Alteration of the strength of the B.C. seems to have little or no influence on the 
change of resistance produced by a given amount of magnetizing force, and therefore we 
/3 7 
may assume that the product of the mean values of - and ^ will fairly represent the 
alteration which would be wrought by a current in the magnetizing coil which would 
suffice to deflect the needle of the tangent galvanometer through one division of the 
scale. 
This product =’0589, and since a division of the iridio-platinum wire corresponds to 
an increase per unit of the resistance of the steel ='000032,'“ and, since also one 
division of the scale of the tangent galvanometer represents a current of '00023, whilst 
the average magnetizing force due to unit current would in the present instance be 
2100x-82x47r 
30 
> we see that the maximum increase of resistance obtained by the mag¬ 
netization was '062 per cent., and that the increase of resistance per unit for unit 
magnetizing force would be 1137X 10 -8 . 
* Of course correction is here, and in all similar cases, made for the resistance of the terminals, which, 
however, with these rods was very small. 
