366 Mr. A. 0. Jolley on the Magnetic Balance 



front of the scale, which consists of a horizontal rod PQ 

 turning about a vertical axis in a heavy base, and furnished 

 with a large milled head G, which can be turned by the 

 observer. This rod is provided with two clamps P and Q, 

 which are attached by two cords to two rings R and V on a 

 similar rod attached to the axis of the magnet NS. If the 

 cords are initially arranged so that the rods PQ and RV are 

 parallel, the position of the magnet is at once determined by 

 the direction of the rod PQ, and it can be turned either by the 

 milled head G, or preferably by holding the two cords ss like 

 reins. 



The advantage of employing a rectilinear filament lamp 

 (such as is made by the Pintsch Gluhlampenfabrik in Berlin) 

 is considerable in practice, as the spot is always visible on 

 the scale even if the torsion-arm is not perfectly balanced 

 horizontally. 



Appendix. 



By the courtesy of M. Cheneveau and the Cambridge 

 Scientific Instrument Co., we have been able to set up and 

 test the performance of one of these balances in the labora- 

 tories of the Northampton Institute. 



The instrument was of the magnetically damped type 

 described above, and was used with a lamp and scale at some 

 two metres distant from the mirror. 



No attempt was made to obtain absolute values of the 

 coefficients of specific magnetization ; but relative deter- 

 minations only were made, using as a standard substance 

 distilled water, and assuming for it the value 



K'=-0'79 x 10- 6 , 



as found by M. Curie and given above. 



The results obtained are set out in the accompanying table, 

 and show some interesting figures. 



The first portion of the table contains figures for a few 

 materials selected quite at random in order to test the 

 behaviour of the balance. Of these the first five are 

 chemically pure liquids, and all exhibit diamagnetic qualities. 



The four samples of aluminium are all magnetic, and we 

 have not been able to get a sample which is less magnetic 

 than the first of these. The eleven samples of brass indicate 

 the range over which the magnetic qualities vary, while some 

 of the samples examined, but not here tabulated, have been 

 too magnetic to be used in the apparatus without changing 

 the suspension. 



It is interesting to note that during some inductance tests 



