582 REPORT— 1901. 



wood, the ' comparison ' coll beiug of copper, and wound close to it on tlie same 

 bobbin. These coils were enclosed in a glass tube and placed within the 

 magnetising coil which was provided with a water-jacket. 



Auxiliary coils of German silver were connected in the other two arms of the 

 bridge so as to increase the sensibility of the arrangement. The magnetisation 

 was determined by the ballistic method. Wires of iron, steel, and nickel were 

 examined. The curves of ' ascending reversals ' were obtained for the change of 

 resistance and for the magnetisation. A comparison of these curves shows the 

 manner in which the change of resistance depends on the magnetisation. The 

 results obtained by this method showed that the change of resistance is not 

 proportional to any single power of the magnetisation, but can be represented by a 

 function of the type al- + bV + cI". 



Hysteresis loops were also obtained showing the effect of cyclic variations 

 of field on the change of resistance and on the magnetisation in the same 

 specimens. These curves show that the change of resistance vanishes in the cycle 

 when the magnetisation vanishes, but the change of resistance shows considerable 

 hysteresis with regard to the magnetisation. 



7. The Injiuence of a Magnetic Field on the Viscosity of Magnetisahle 

 Liqtiids. By Professor A. Gray, F.R.S. 



The Influence of a Magnetic Field on the Viscosity of Magnetisahle 

 Solids. By Professor A. Gray, F.R.S. 



9. Magnetisation of Electrolytic Nickel. 

 By James W. Peck and Robert A. Houstoun. 



An account is given of experiments in progress to determine the magnetic 

 quality of electrolytically deposited nickel. The method of deposition is described, 

 and the difficulty of getting adherent deposits of sufficient thickness is pointed 

 out. Magnetic measurements (by the ballistic atep-by-step method) made upon 

 the nickel are given, and for purposes of comparison similar measurements for 

 specially pure nickel wires are made. These wires contained only from 0'25 per 

 cent, to 042 per cent, of impurity (chiefly iron). Values for II, I, B, k, fi are 

 given ; and hysteresis cycles and permeability carves are drawn out. A moving 

 coil galvanometer (as recommended by Ewing) is used for many of the ballistic 

 measurements, and is found to be very convenient. 



10. A Neio Form of Permeameter. By Professor F. G. Baily, M.A. 



The apparatus depends on the measurement of the ratio of B to H in the 

 sample. A complete magnetic circuit is formed bv two lengths of the sample 

 ioined bv short iron blocks at the ends. Magnetising coils are placed round the 

 sample. " In one of the l^locks is a narrow gap per])endicular to the direction of the 

 lines of force. Above this is pivoted a pair of astatic magnets. The lower 

 mao-net is intluenced by the difference of magnetic potential between the two sides 

 of the gap, the force being proportional to B. Round the upper magnet is placed 

 a small coil in series with the main magnetising coils, which acts on the magnet 

 with a force proportional to 11. Using the principle of the sine galvanometer, the 

 Coil is rotated until the two forces are balanced, the position of the magnet system 



being along the line of the gap. Then /:i = ^ = f{6). The coil is shaped to give 



an almost uniform scale through some 80° of arc, and the permeability is read 

 directly on the scaler 



