l6 BULLETIN OF THE LABORATORIES 



wave-length is much shorter in the hquid, ( only one-ninth as much in 

 water as in air), it was possible to obtain as many as four nodal points 

 within a vessel 78 cm. long. The details of this work with liquids — 

 water and alcohol— are given in the recent paper in Wiedemann's 

 Annalen before referred to. 



Since the above work was done Drude has published a paper ^ on 

 the same subject giving preference to the exciter described by 

 Blondlot over that of Lecher. I have accordingly made and used 

 the Blondlot exciter shown in Fig. 3. 



Fig. 3. 



In this there are no plates, but the inner ends of the long paral- 

 lel wires are joined by the circularly-curved wire of the figure. With- 

 in this wire and separated from it by only a few millimeters is the pair 

 of primary exciters, P, P\ bent to form arcs of a circle concentric with 

 the curve of the surrounding wire, and carrying zinc balls for a spark 

 gap at the inner ends. These exciters are connected directly to the 

 secondary terminals of an induction coil. This form of exciter gave 

 satisfactory results, but I have done too little work with it to make 

 comparison with that of Lecher. I have also made successful use of 

 the suggestion of Drude to use a Righi resonator, /. e. a strip of mirror 

 amalgam with a narrow slit cut across the middle, as a means of locat- 

 ing nodes and loops in parallel wires. In a later apparatus of the 

 Lecher type I have used balls of zinc instead of brass for the spark gap. 



Neither Rubens nor Cohn seem to have found it necessary to pro- 

 tect the wires leading to the bolometer from electro-magnetic distur- 

 bances, but I have found it important. This was accomplished by 

 enclosing them in long glass tubes which were in turn surrounded by 

 a brass tube. 



' P. Drude, Wied. Annalen, Vol. LV, p. 633, (1895.) 



