Magnetic Hysteresis loss in Straight Iron Strips. 265 



investigation was concerned with the study of the mode in 

 which this induction density varies from point to point in the 

 length of a bundle of iron strips or iron wire or steel rods of 

 various lengths and diameters, thus placed in the centre of a 

 long magnetizing solenoid. 



A magnetizing coil was prepared, wound on a paper tube, 

 5 7 centimetres in internal diameter and 99 centimetres long. 

 On this tube was wound, in three layers, a coil of 1235 turns 

 of cotton-covered copper wire, '064: inch diameter or of 

 No. 16 size S.W.G. The resistance of this coil was 

 1069 ohms at 15° C. 



The number of turns per centimetre length of this coil was 

 12*47. Hence since the interior central field is 47r/10 times 

 the ampere turns per unit of length of the coil, we have thus 

 the value of the field H in the central regions of the interior 

 of this bobbin given by the equation 



H = 15-66 A, 



where A is the ampere current through the coil. 



The secondary or exploring coil consisted of a flat bobbin 

 wound up of silk-covered copper wire '0024 inch in diameter 

 and having 2000 turns ; the thickness or length of the bobbin 

 being 0*7 centimetre and the external diameter about 

 4*5 centimetres. 



The exploring coil was wound on a circular ebonite former 

 having a rectangular hole in it so as to closely fit the bundle 

 of iron strips to be used, but at the same time it could be slid 

 along the bundle. 



The voltmeter used with it was one of Professor Ayrton's 

 low-reading electrostatic instruments of the idiostatic type 

 and read from 1 to 25 volts, the reading being taken by a 

 mirror and scale. The voltmeter was calibrated when 

 required by means of standard cells or a potentiometer. 



The first experiments were conducted with strips of trans- 

 former iron, kindly furnished to us by Messrs. Sankey. 

 This sheet iron was '0121 of an inch or - 0307 of a centimetre 

 in thickness and the strips were each one inch or 2 "54 centi- 

 metres wide. The strips used were of various lengths : 

 60 centimetres, 30 centimetres, 15 centimetres, down to 

 5 centimetres. A bundle I (see diagram) of a certain number 

 of strips was made and the secondary coil v slipped on to it. 

 The magnetizing coil C was then traversed by an alternating 

 current having a ft-equency of 80 ~, and the R.M.IS. (root 

 mean square) value of the current was read by a dynamometer 

 D or Kelvin balance. 



The electrostatic voltmeter V being connected to the ends of 



