4294 H. A: Rowland—Magnetic Permeability, and the 
and gives the height of the curve (see figure); 6 establishes 
the inclination of the diameter TS; H is the line Po and 
depends upon the distance PR. The following equation, 
adapted to degrees and fractions of a degree, is the equation 
from which the values of y in table I were calculated : 
Q+10°9414+5000) 
1 | ee 
000° 
The relation between Q and M is readily obtained from this 
p= 2475" sin( 
equation by substituting the value of yu, which is rena These 
equations can in general be solved only by successive approxi- 
mations, but in the first case where Q and ys are involved, we 
may solve with reference to Q. This formula has been tried 
for all the tables, giving the proper values to the constants, 
and agrees with them all very exactly. 
On plotting any table in this way and measuring the dis- 
tance o R, we have the maximum of magnetization. 
I have deduced the constants in the formula for no less than 
twelve cases of iron and two of nickel, and find them to vaty 
between wide limits: the value of B, which is the maximum 
value of the permeability, varies between 5500 for the best 
orway iron very carefully annealed and 830 for Stubs’ steel 
of such temper as the wire is when bought, but of course this 
would be much less for hardened steel. 
I have also obtained the maximum value of Qin many cases, 
and find it for good, but not pure, iron to be about 175,000 an 
for nickel 63,000 ; that is, the magnetization of iron can never 
square meter of section, which is gq absolute units of force, oF 
Q? 
178 240 000 
which gives 177 for Q = 175,000 and 22-9 for Q = 68,00. 
ence we may conclude that the greatest weight which can Pts 
sustained by an electro-magnet with an infinite edges 
iron 854lbs. per square inch of section, and for nickel 
* Treatise on Electricity and Magnetism, vol. it, p. 256. 
lbs. per sq. in. 
