Determinations of Magnetic Susceptibility. 



407 



coil it was read and measured by this galvanometer. The weight W" 

 was simply used to balance the weight of the coil. 



It will easily be seen from the arrangements of cords, pulleys, &c, 

 that the wire, besides being kept straight, can be raised or lowered 

 through any desired distance within a range of about 4 metres ; 

 and further, that when the wire is moved up or down the coil follows 

 the movements, keeping its position with reference to the former un- 

 altered. For the purpose of observing the position of the wire or the 

 coil with great facility at any instant with inference to the line on a 

 level with the magnetometer needle, there is provided, alongside the 

 wire and coil, a scale divided into centimetres, and fixed to a wooden 

 upright. 



The orderly and systematic way in which the experiments were 

 performed may be described generally thus : — A weight, the amount 

 of which was different for different specimens of the wire as will 

 be presently stated, was put on and taken off the wire, whilst the 

 magnetising force was in action, about ten times in succession (this 

 operation of successive application and removals of a weight will be 

 hereafter called, for brevity, " ons and offs "), half a kilogramme being 

 always on ; then the wire, having been first placed so high up that its 

 effect and that of the coil on the magnetometer was scarcely visible, 

 was lowered 2 centims. by 2 centims., until it was so low down 

 that little or no effect of the wire and coil was observable on the 

 magnetometer, while the deflections of the magnetometer needle were 

 noted for all the positions of the wire and coil. This process was 

 followed in the case of all the wires, except the hard-tempered wire, 

 and all the magnetising forces used, unless otherwise stated. It will 

 be needless to enter into the discussion of the details of the object of 

 subjecting the wire to the operations of " ons and offs," as they will 

 be, I hope, shortly communicated to the Royal Society or elsewhere ; 

 suffice it to point out here that on commencing the preliminary 

 experiments, it was soon discovered that in the first instance the wire 

 was very irregularly magnetised, but that the effect of subjecting the 

 wire, while under the influence of the vertical force, to the applica- 

 tion and removal of a pull a certain number of times in succession, 

 was to remove all the irregularities as to magnetisation, besides pro- 

 ducing an enormous augmentation of its magnetism. 



The results are given in the Tables I to IV. The general explana- 

 tion of these and other accompanying tables is, that the " Distances" 

 mean the distances of the centre of the wire from the level of the 

 magnetometer needle, those distances measured from their level up- 

 wards being reckoned positive, and those measured downwards nega- 

 tive ; while the " Deflections " mean the corresponding deflections of 

 the needle in the scale-divisions — those deflections indicating the 

 repulsion of the north-seeking pole, or red end of the needle, being 



