184 Mr. E. Rutherford. A Magnetic Detector of 



ished on more complete magnetisation, until at an induction of about 

 20,000 it became very small with every indication of disappearing 

 altogether. Soft iron and hard steel gave very similar curves, and 

 in both the curve of hysteresis-induction cut the curve obtained from 

 the values in an alternating field at a point just before the maxi- 

 mum. The result fully bears out the deduction from the theory, 

 and proves in addition that hysteresis is not sensibly due to anything 

 of the nature of mechanical restraint of the molecules. The form 

 of the curve also gives clear indications of the three stages of molecular 

 movement, the first stage giving a slowly rising curve, the second a 

 straight rapid rise, and the third a straight and much more rapid 

 descent. 



Further experiments were carried out on the effect of speed of 

 rotation. In an alternating field the speed of reversal has been shown 

 to be without sensible effect on the hysteresis, and theory points to 

 this result as a natural deduction. The above apparatus was well 

 adapted for testing the matter, since the hysteresis per reversal could 

 be read at each instant independently of the speed. From an ex- 

 tremely slow speed up to 70 revolutions per second no definite 

 change was found in the value of the hysteresis. At the same time 

 several small modifications were noted, produced by rapid variations 

 in the speed of rotation or magnetising force. The effect lasted 

 through many revolutions, but ultimately the same steady condition 

 was arrived at. At a,nd near the maximum value the hysteresis was 

 very variable. The effects were much more marked in soft iron 

 than in hard steel, as would be anticipated from the theory of their 

 constitution. 



The experiments in their verification of an untried deduction form 

 a strong proof of the validity of the molecular theory of magnetism, 

 and throw some light on the nature of the molecular complex and of 

 the interactions which take place therein. 



"A Magnetic Detector of Electrical Waves and some of its 

 Applications." By E. RUTHERFORD, M.A., 1851 Exhibition 

 Science Scholar, New Zealand University, Trinity College, 

 Cambridge. Communicated by Professor J. J. THOMSON, 

 F.R.S. Received June 11, Read June 18, 1896. 



(Abstract.) 



The effect of Leyden jar discharges on the magnetisation of steel 

 needles is investigated, and it is shown that the demagnetisation of 

 strongly magnetised steel needles offers a simple and convenient 

 means for detecting and comparing currents of great rapidity of 

 alternation. 



