1904.] A New Method of Detecting Electrical Oscillations. 121 



was also tested with an alternating current of about 100 periods 

 per second in place of the oscillations, with the effect that the normal 

 hysteresis deflection was almost entirely wiped out. 



Various other forms were also tried with indifferent results, when it 

 occurred to us that there would be advantages in passing the oscilla- 

 tions through the magnetic material itself, making it of magnetic 

 wire. A small bobbin was therefore wound with insulated soft iron 

 wire, and the ends soldered to the upper and lower halves of the 

 spindle, which was itself divided at the centre, the upper half bearing 

 the controlling spring, and the lower dipping into mercury, from 

 which a connection led to the other terminal. On passing oscillations 

 through this winding, a remarkable and unexpected result was 

 obtained. The change of deflection was much more marked than in the 

 former experiments, and was in the opposite sense, indicating an 

 increase of hysteresis while oscillations were present. Afterwards, 

 hard steel wire was substituted for the soft iron, and a very great 

 increase in the effect was observed, still in the same direction — that of 

 increase of hysteresis. 



Owing to these encouraging results, it was decided to continue the 

 experiments in this direction, abandoning the older form, in which a 

 decrease of hysteresis was dealt with. The first bobbin constructed was 

 about T 5 g- inch in external diameter, and had a vertical wire space of 

 \ inch. The winding was a single No. 32-gauge iron wire, double 

 cotton-covered, wound straight round from beginning to end. Later, 

 No. 40 and No. 46 steel wires were employed, of which the latter gave 

 the best results. 



It was soon noticed that any method of increasing the oscillatory 

 current in the wires, as by winding the bobbin with two wires having 

 a slightly unequal number of turns, was of advantage in giving a 

 larger deflection. Later a fine copper wire secondary, wound on 

 the bobbin parallel to the magnetic wire, was tried, first with the 

 ends insulated, and then with the ends soldered together. A marked 

 increase in deflection was observed when the secondary was closed, 

 showing that the magnetic nature of the wire itself was influential. 

 Accordingly, a bobbin was then wound with insulated steel wire, 

 doubled back on itself. This non-inductive winding gave by far the 

 best results hitherto attained, and is now used, except when special 

 results are required. 



The instrument, though described as a detector of electrical oscilla- 

 tions, may be said to measure rather than detect, giving quantitative as 

 well as qualitative results, and being capable of regulation from a 

 sensibility of the same order as that of an average coherer down 

 to practical insensibility to powerful sparks in the same room. 



In the instrument, as shown in the figure, the electro-magnet takes 

 the form of a ring capable of moving round a vertical axis, and is 



K 2 



