990 
PEOFESSOE J. A. EWING AND MISS H. G. KLAASSEN 
The use of the coil C made the magnetic induction, as well as the magnetizing force, 
depend for its interpretation in absolute measure on the standard furnished by the 
Kelvin balance. The resistance was a frame of platinoid wire, wound for these 
experiments ; Kg was, in the first instance, a liquid slide consisting of amalgamated zinc 
plates, immersed in a jar containing solution of zinc-sulphate, but in the later experi¬ 
ments we found that a Yarley carbon resistance, consisting of a pile of discs adjustable 
by compression, formed a very convenient substitute, especially when supplemented 
by short shunts of platinoid for the lower values of Rg. 
All the samples tested in this set of experiments were arranged in the form of rings, 
wnth a mean diameter, generally, of about 10 centims., and an area of cross-section of 
from one to two square centims. The magnetizing coil was wound uniformly round 
the whole ring, in a single layer or in two layers. A few turns of wire, wound out¬ 
side of that, formed the secondary or induction coil, the number of these turns being 
chosen so that reversal of the strongest magnetization produced as large a throw as 
could conveniently be read on the ballistic galvanometer. In several instances pans 
of rings were prepared, exactly alike in all respects, for the purpose of making certain 
special tests which will be described later. 
With each sample a series of cycles were determined, generally ten or twelve, 
beginning with one in which the limiting magnetization was strong, and working 
down to cycles on which the range was so small that the efiects of hysteresis nearly 
disappeared. In the case of one or two samples a supplementary examination of the 
smaller cycles was made on a finer scale, by means of another secondary coil with a 
considerably larger number of turns, while the scale of the current galvanometer was 
at the same time altered by using a weaker shunt. We shall now give the results of 
the tests in detail. 
Ring I.—In this ring the core was of fine iron wire, insulated by a winding of 
cotton. The diameter of the wire was 0'02475 centim. It was supplied (by Messrs. 
Glover) as a specimen of soft iron, but the tests showed that it had either not been 
softened, or had been insufficiently softened after its last passage through the draw- 
plate, the curve of magnetization presenting, to some extent, the characteristics of 
those for unannealed metal. Eleven cycles were examined; the results are stated 
below and are shown by the curves of fig. 4 (Plate 34 ). Tlie figures give the magnetic 
force H and the magnetic induction B, both in C.G.S. units. 
