692 REPORT— 1893. 



The lowest and uppermost plates are connected by fine wires to the two pairs of 

 quadrants of my quadrant electrometer, and it is generally convenient to allow the 

 lowest to lie uninsulated on an ordinary table and to connect it metallically with 

 the outer case of the electrometer. 



To make an experiment, (1) connect the two fine wires metallically, and let 

 the electrometer needle settle to its metallic zero. 



(2) Break the connection between the two tine wires, and let a weight of a 

 few decigrammes or kilogrammes fall from a height of a few millimetres above the 

 upper plate and rest on this plate. A startlingly great deflection of the electrometer 

 needle is produced. The insulation of the indiarubber supports and of the quad- 

 rants in the electrometer ought to be so good as to allow the needle to come to 

 rest, and the steady deflection to be observed, before there is any considerable loss. 

 If, for example, the plates are placed with their zinc faces up, the application of 

 the weight causes positive electricity to come from the lower face of the upper- 

 most plate, and to deposit itself over the upper surface of plate and weight, and on 

 the electrode and pair of quadrants connected with it. 



8. Electrical Interference Phenomena someivJiat Analogous to Newton^ s Rings, 

 hut exhibited hj Waves in Wires. By Edwin H. Barton, B.Sc. 



Ilerr von Geitler, > while experimenting in 1892 with electrical waves passing 

 along a pair of long parallel wires, noticed the following phenomena : — 

 if the wires at any part of their length ware either 



(1) replaced by others thicker or thinner than the normal wires, as shown 



at A, fig. 1, or 



(2) arranged nearer together or farther apart than their normal distauce, as 



shown at B and C, fig. 1, then, in any of these cases, a partial 

 reflection of the electrical waves occurred at such place of change in 

 the wires. 



Fig. 1. — Arrangements which produce partial reflection. 



Von Geitler then made further observations of what occurred when a con- 

 denser was attached at a sinr/le point of each wire, as at D, fig. 1, but did not qucaiti- 

 taticely examine the reflections of the waves produced by the changes first named. 

 This I commenced to do, as it seemed interesting to ascertain if theory and experi- 

 ment agreed quantitatively. Now it is easy to see that with a finite length ot the 

 altered or abnormal part of the wires we should have not a single reflection merely, 

 but trvo places at which reflections would occur, namely, the beginning and the end 

 of this abnormal part. I thus anticipated that interference phenomena would 

 •occur, and that if the length of the abnormal part were gradually increased, the 

 intensity of the transmitted waves would periodically increase and" decrease. 



The best arrangement which I have obtained for observing these interference 

 ■effects is that diagramatically shown in fig. 2. 



Explanation of Fig. 2. 



I. Induction coil worked by two secondary cells. 



G. Spark gap. 



PG P'. Primary oscillator which emits waves 9 m. long. 



GP = GP; = lm. long. 



PP'. Discs of zinc plates 40 cm. diameter. 



' Wied. Ann., vol. 49, 1893, pp. 184-195 ; Ueler Eeflexion eleUrisclicr Dralitivdlen, 

 von J. Ritter von Geitler. 



