1904.] A New Method of Detecting Electrical Oscillations. 123 



permanent magnet system giving a similar field. A structure is 

 built up, external to the magnet, to support the vessel containing the 

 pivoted bobbin and its centreing arrangements. The bobbin itself is 

 made of bone, and is about 2 inches long. It is provided with a 

 steel spindle at each end bearing in a jewel hole, the two halves of the 

 spindle being insulated from one another. The winding, which 

 is, as far as possible, non-inductive, consists of about 500 turns of 

 No. 46-gauge hard-drawn steel wire, insulated with silk. The bobbin 

 is immersed in petroleum, or a mixture of petroleum with thicker 

 mineral oil, which serves the double purpose of fortifying the insula- 

 tion, and giving the damping effect necessary to steady the deflection 

 due to the drag of the revolving magnet. Eeadings are taken by 

 means of a spot of light, as with speaking mirror galvanometers, 

 but a siphon-recording attachment has' been fitted, and any form of 

 contact for working a relay could be employed. 



The detector, as before mentioned, gives quantitative readings, and, 

 in some cases, the deflection may be too large to be easily read by the 

 scale. For this purpose a variable shunt is provided, by which the 

 deflection can be regulated. 



For the purpose of wireless telegraphy, the instrument has the 

 advantage of giving metrical effects. The benefit of this in facilitating 

 tuning, and in other respects, need not be insisted upon. 



From the physical point of view, the augmentation of hysteresis is 

 interesting and unlooked for. It is probably to be ascribed to this, 

 that the oscillatory circular magnetisation facilitates the longitudinal 

 magnetising process, enabling the steel to take up a much larger 

 magnetisation at each reversal than it would otherwise take, and thus 

 indirectly augmenting the hysteresis to such an extent that the direct 

 influence of the oscillations in reducing it is overpowered. The net 

 result appears to be dependent on two antagonistic influences, and, in 

 fine steel wire, under the conditions of our experiments, the influence 

 making for increased hysteresis, as a result of the increased range of 

 magnetic induction, is much the more powerful. 



