CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL 

 LABORATORY, HARVARD UNIVERSITY. 



THE MAGNETIC PERMEABILITIES AT LOW EXCITATIONS 

 OF TWO KINDS OF VERY PURE SOFT IRON. 



By B. Osgood Peirce. 



Presented May 11, 1910. Received August 26, 1910. 



More than a year ago, I had occasion to study the magnetic proper- 

 ties under very high excitations of a piece of Norway iron^ (P), which 

 proved when analyzed to be extraordinarily pure. The tests made in 

 the Chemical Laboratory of Harvard University by Mr. E. R. Riegel, 

 for nickel, cobalt, tungsten, and even manganese, as well as for the 

 metals of Groups IV and V, were all negative. There was less than 

 0.03 per cent of carbon, less than 0.047 per cent of phosphorus, less 

 than 0.03 per cent of silicon, and less than 0.003 per cent of sulphur. 

 A slender rod of this remarkable iron, of which we had originally a 

 round bar five centimeters in diameter and thirty-four centimeters 

 long, had, when annealed, an extremely high permeability under exci- 

 tations above 200, but, because of the local reluctance at the joints, 

 it did not prove easy to determine the permeability of this rod in a 

 yoke at low excitations. The metal showed to the eye a fibrous struc- 

 ture with striae parallel to the length of the bar, as if minute quanti- 

 ties of scale had been included in the bar in the rolling ; and it seemed 

 likely that the specific reluctance to magnetization across the grain of 

 the iron, would be greater than to magnetization parallel to the grain. 

 Under these circumstances it was probable that the permeability of a 

 ring, so cut from the metal that its axis should be parallel to the grain, 

 would appear low. It happened, however, that I had two such rings, 

 but that there was not enough of the iron left to make rings with axes 

 perpendicular to the grain, and I was forced to get what information 

 I could from them, though it soon became evident that for excitations 

 above five gausses the permeability fell below what commercial Norway 

 iron should show. 



* American Journal of Science, 28, July, 1909, 



