10 
the end of a cylindrical shaft of best Kirkstall drawn iron, 
which was then well annealed, and turned into a ring of 
circular section (diameter of section is about Jin.). The 
metal is of fair quality and softness, but not so ductile as 
the best Lowmoor iron. The mean external diameter of 
the ring is 14*6 cm,, the mean diameter of section is *95 cm., 
and its weight is 230*172 grams. Another ring was made 
by cutting a disc out of an iron plate, and then treating 
this disc like the previous one. 
Attention was also given to the following point — whether 
by some process a ring, which had been raised to nearly 
the maximum of magnetism, could be brought back to its 
original state, so that a fresh series of observations of the 
magnetic induction and the permeability should not differ 
from the previous set. With regard to this, Kowland says, 
in the paper quoted above, ‘'To get the normal curve of 
permeability, the ring must only be used once ; and then no 
more current must be allowed to pass through the helix 
than that with which we are experimenting at the time. 
If by accident a stronger current passes, permanent mag- 
netism is given to the ring, which entirely changes the first 
part of the curve.” 
The method of sending alternate currents (gradually 
diminishing from the maximum used before, until they 
become evanescent) through the primary winding was used, 
and found to give good results. 
The ring was wound as follows—it was covered with silk 
riband, soaked in melted parafiin wax ; on this 334 turns of 
No. 20 double silk covered copper were wound, the whole 
was covered with silk riband and paraffined, and on this 
were wound three separate coils, one of 200 turns, and two 
of 100 turns, of No. 24 double silk covered copper wire. 
The whole was then immersed for a moment in melted 
paraffin wax. The resistances of these coils were measured 
