986 
PROFESSOE J. A. EWING AND MISS H. G. KLAASSEN 
ViGNOLES.-''* and by Mr, C. P. SxEiNMETZ.t Notwithstanding, however, the increased 
interest which now attaches to the matter in consequence of its practical bearing, the 
available data are still meagre. By way of adding to them, we have made a detailed 
examination of some ten samples of wire and sheet iron, arranged in the form of 
rings to be operated on by the ballistic method. 
In the former tests, referred to above, the method used was to make direct observa¬ 
tions with a magnetometer, the samples being then long, straight pieces of wire. 
When the metal to be examined is in the form of wire, which may be taken long 
enough to secure j^ractical endlessness, or of rods or bars big enough to be turned 
down into ellipsoids, the direct magnetometric method is entirely suitable. Several 
of our samples, however, were to be cut out of plate or sheet metal, such as is now 
largely used in the manufacture of transformers; and for this reason, as well as 
because direct measurements were to be made of the heating effect of magnetic 
reversals (which made ring samples most eligible), the ballistic method was selected, 
and a somewhat novel form was given to it, to allow points on the cyclic curve to be 
accurately and conveniently determined by its means. 
In the paper already cited, some ballistic observations of magnetic cycles were 
described, in which the successive points on the cycle were determined by summing 
the ballistic effect of successive steps, in each of which the magnetic force underwent 
a small sudden change. This method is, at the best, laborious, and requires great 
point depends on that of the points before it, though at the end of the process a 
check may be applied by comparing the ballistic effect of a sudden reversal with the 
sum of the effects of successive steps. There is an obvious advantage in making the 
determination of each point independent of the previous readings of the ballistic gal¬ 
vanometer, and, recognizing this, Messrs. Evershed and Yignoles introduced, in 
their experiments, the plan of reading each point by a single step from the terminal 
condition of magnetization represented by one or other extremity of the cycle. They 
wound their ring with two coils, through one of which a constant current was main¬ 
tained ; through the other coil a current, opposite in magnetizing quality, could he 
passed, and its strength could be varied up to a maximum which made its ampere- 
turns just twice the ampere-turns of the other coil. Then, when current flowed in 
the first coil only, the magnetization had its extreme positive value. By suddenly 
applying a current in the second coil, it was altered to any value between the positive 
and negative extremes. The use of two currents is an undesirable complication, 
especially as the symmetry of the resulting curves depends on the exactness with 
which the magnetizing effect of the one is adjusted to be, at its maximum, just twice 
that of the other. We have devised, and used throughout all these experiments, a 
method which, while requiring only one current and one magnetizing coil, retains the 
* Eyershed and Vignoles, ‘ The Electrician,’ May 15, 1891. 
t Steinmetz, ‘ Transactions of the American Institute of Electi-ical Engineers,’ vol. 9, No. 1. 
