﻿428 Mr. C. E. St. John on Wave-lengths 



which is carefully adjusted to resonance before any other 

 measurements are made. 



For determining the occurrence of resonance and for ex- 

 ploring the wires to obtain the wave form, the bolometer as 

 described by Paalzow and Rubens * was used in connexion 

 with Eubens's f adaptation of it. The exploring terminals of 

 the bolometer are shown at P, fig. 2. They consist of two 



Fig. 2. 



capillary glass tubes set in a frame of wood; the tubes slide 

 over the wires to be explored, and around each tube is 

 wrapped, by a single turn, one of the lead wires to the 

 bolometer. Electric oscillations in the secondary circuit 

 cause inductively alternating currents along the lead wires 

 through one arm of a balanced Wheatstone bridge, which 

 forms the bolometer. This arm of the bridge is made of fine 

 iron wire, and so arranged that the bridge current and these 

 oscillating currents traverse it without affecting each other. 

 The bridge is thrown out of balance by the increase of resist- 

 ance caused by the heat generated from the alternating 

 currents, and a corresponding throw of the galvanometer is 

 produced. 



To adjust the circuit to resonance the exploring terminals 

 were placed at P S (fig. 1). The induction-coil was put in 

 action, and the reading of the bolometer taken for this length 

 of wire. A few centimetres of wire were cut off and the reading 

 again taken. This operation was repeated until a maximum 



* "Anwendung des bolometrischen Princips auf electrische Messungen," 

 Wied. Ann. xxxrii. p. 529. 



t " Ueber stehende electrische Wellen in Drahten und deren Messung," 

 Ibid. xlii. p. 154. 



