OF DENISON UNIVERSITY. 9 



the stationary sound-waves in a vibrating stretched string. As in 

 Lecher's experiments, a small Geissler tube without electrodes, placed 

 between the remote ends of the parallel wires, glowed brilliantly. 



A short wire placed across the parallel wires in general caused the 

 light to cease, but positions could be found such that the tube still 

 continued to glow. Three such positions were found with the appara- 

 tus used. These were separated by etpial intervals and marked nodal 

 positions, any interval giving the half wave-length of the undulations 

 in the wires. The ends of the wires and of the secondary plates form 

 ventral segments in the resonance system. H. Rubens^ had succeeded 



Fig. I. 



in measuring not only the length but the form and amplitude of such 

 waves by use of the instrument devised by Paalzow and himself and 

 named the "dynamo-bolometer." I used the same instrument em- 

 ployed by Rubens in his study of stationary waves in wires. Fig. 2 

 shows its construction. -^1 R'l R,s R\ are the resistances of a balanced 

 Wheatstone bridge. Two of these, R\ R 2, are themselves balanced 

 bridges, each of their four arms being a very fine iron wire about 10 

 cm long and of seven ohms resistance. Suppose the whole system 

 balanced, and a weak but steady current supplied by the battery B. 

 The galvanometer shows no deflection. Evidently if alternating cur- 

 rents produced by electrical oscillations enter by the wires ww' they 

 will circulate only in the minor bridge R 2, but will disturb the balance 

 of the main bridge by the heating effect in R 2. This disturbance, if 



' H. Rubens, Wied. Annalen, Vol. XLII, p. 154, (1891.) 



