214 J. A. POLLOCK. 
instances. In the case of straight wires two small insulat- 
ing tubes are placed symmetrically on the wire usually 
about 200 cms. apart. Hach tube is encircled by a single 
loop of wire, the loops being attached by fine wires to 
mercury cups in a piece of hard rubber placed a little behind 
the middle of the straight wire, so that the ends of the 
solenoid of the detector may be joined to them. Readings 
with the detector are now taken on discharging the con- 
denser, for various lengths of the parallel wires. At each 
adjustment of the length, the position of the bridge on the 
wires and the distance between the condenser plates are 
altered, by reference to the curves obtained in the pre- 
liminary investigation, so that the condenser circuit is 
always kept in tune with the parallel wire system. When 
the amplitude of the vibration in the straight wire isa 
maximum under these circumstances, as determined by the 
observations with the detector, the wave length of the 
vibration connected with the straight wire is considered to 
be the same as that associated with the rectangle formed 
by the parallel wires and the two bridges. Hxperiments 
with the other circuits have been made in a similar manner. 
A complete set of results was obtained by this method. 
A. second plan has been to set the condenser circuit and 
the parallel wire system in tune with each other and keep- 
ing this part of the apparatus fixed to alter the length 
of the third circuit by successive steps of 10 or 20 cms. 
From a plot of the observations of the disturbances in 
the third circuit, its length when it is in tune with the 
rectangle may be found. This method is more satisfactory 
than the former one, in that each successive step involves 
the alteration of only one of three circuits instead of two 
as in that case. 
In repeating the experiments by this method the plots of 
the observations showed more decided maxima.. When the 
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