LAWS AND WARREN. — HYSTERESIS. 495 



bility was very low, it would be necessary to apply a correction for this 

 unoccupied area. The values of B were calculated by the formula 



E^R D 



~ 20 A NnE^iy"- ' 



D is the deflection corresponding to the value of B to be found. R is 

 the resistance in circuit R h ; N, the number of turns on B winding. 

 n, the number of revolutions per second. A is the area of the iron in- 

 cluded in the B windings. D^ is the deflection of the galvanometer 

 when an E.M.F. of magnitude E^ and a resistance R^ are inserted in 

 the circuit R h, the dynamo turning at the normal rate. 



The furnace used for heating the specimen was built of fire brick, 

 the external diameter was about 36 inches, height 18 inches. Inside 

 the fire brick was a layer of asbestos wool 2^ inches thick, kept in place 

 by asbestos board, which was protected by thin sheet iron. The box 

 containing the specimen was made of asbestos board about IJ- inches 

 in thickness, and lined with retort cement. During the tests it was 

 tightly closed. The furnace was heated by three blast jets made of 

 gas pipe, the external tubes were | inch inside diameter, the inner 

 tube I inch. The supplies of gas and air were regulated by slide 

 valves. The jets were directed into the furnace tangentially and with 

 a slight upward inclination, the eff"ect being to establish a good circu- 

 lation and keep the interior of the furnace at a uniform temperature. 



The specimen upon which the following tests were made was com- 

 posed of so called French steel, which showed on analysis the follow- 

 ing impurities : — 



Manganese 0.535 per cent. 



Phosphorus 0.013 " 



Silicon 0.085 " 



Sulphur 0.018 " 



Carbon 0.970 



u 



The mass of iron employed was 628 grams. From this material, 

 which was four one-thousandths of an inch thick, rings of 3 inches' out- 

 side and 2 inches' inside diameter were stamped, and the specimen 

 formed by piling them. Each was insulated from its neighbors by a 

 layer of pipe clay, applied as a sort of paint, the clay having been 

 moistened with alcohol. Every tenth layer was insulated with mica. 

 The pile so formed was wrapped with asbestos cloth, and the mag- 

 netizing coil of 36 turns of No, 14 copper wire wound on. The wire 

 was insulated by winding it with asbestos twine. Interwound with 



