214 Messrs. Trowbridge and Duane on 



C 



As a means of ascertaining when the circuits were in 

 resonance, and of investigating the form of the wave in the 

 secondary circuit, a bolometer similar to that designed by 

 Paalzow and Rubens* was used. 



The bolometer as an instrument for measuring electric 

 waves is so well known, that it is not necessary to state here 

 more than its fundamental principles. It consists essentially 

 of a well-balanced Wheatstone bridge to one of the arms of 

 which are metallically connected two small conductors. 

 These conductors are brought near the circuit to be tested, 

 and the oscillating charges induced in them and sent through 

 the arm of the Wheatstone bridge develop enough heat to 

 throw the bridge out of balance. By moving the conductors 

 along the circuit different deflexions are produced according to 

 the magnitude of the charges on the wire in their neighbour- 

 hood, and thus an excellent estimate of the wave formation 

 can be obtained. In the present case the conductors that 

 were brought near the secondary circuit consisted of two 

 pieces of wire insulated with rubber, bent into circles of about 

 2 centim. radius, and fastened to a bit of pine-wood by means 

 of a heavy coating of paraffin. The two wires of the 

 secondary circuit passed through holes in this bit of wood in 

 such a manner as to pass through the centres of the two 

 circles. In the early part of the investigation the bolometer 

 and galvanoscope were placed at a sufficient distance from 

 the oscillating circuits to prevent any direct action of 

 one on the other, and the leads running from the circular 

 conductors to the bolometer consisted of long fine wires. 

 Later, when longer circuits and longer waves were experi- 

 mented with_, great inconvenience was experienced from the 

 long leads, since their relative position had considerable effect 

 upon the galvanoscope deflexions. In order to obviate this 

 difficulty short leads of heavily insulated wire were used, and 

 the bolometer was placed on wheels and moved along from 

 place to place. A bolometric study of the circuit just described 

 showed the character of the oscillation to be that mentioned, 

 namely, nodes at the points J, and GH, and a ventral seg- 

 ment at KL. A careful run was made from one end of the 

 circuit to the other, which furnished data from which a very 

 regular curve was drawn. 



The insertion of a small spark-gap (1 millim.-3 millim.) 

 at the point in the secondary circuit marked J (fig. 1) had no 

 appreciable effect upon the position of the nodal point GrH, 

 or of the point of maximum accumulation KL. The form of 



* Anwendung des bolometrisclien Princips auf electrische Messungen," 

 Wied. Ann. xxxvii. p. 529. 



