220 J. A. POLLOCK, 
tube on the straight wire; (2) wires each 40 cms. long 
soldered to the straight wire; (3) wires 25 cms. long 
soldered to the straight wire; (4) wires 10 cms. long sol- 
dered to the straight wire. In each case the observations 
gave the same result, the straight wire 400 cms. long being 
in tune with a rectangle 955 cms. in perimeter. 
Further an exhaustive comparison has been made between 
the results given by the solenoidal detector and those 
obtained with Rutherford’s longitudinal detector. The 
latter was made of a piece of pianoforte steel wire 5°5 
cms. long, which had been dissolved in acid until its diameter 
was 0°014 cms. The ends of the steel wire were soldered 
to two pieces of copper wire, each 1 cm. long and 0°33 cms. 
in diameter. The wire was then firmly fixed by means of | 
the copper ends in a glass tube, the copper pieces project- 
ing a few millimetres beyond the ends of the tube. In an 
experiment the detector, after being magnetised to satur- 
ation, replaced a similar length cut from the middle portion 
of the circuit under investigation. Connection was made 
by amalgamating the copper ends which were in contact, 
excess of mercury always being present. The magnitude 
of the disturbance in the third circuit is estimated by its 
demagnetising effect on the steel wire, the detector being 
placed after magnetisation and demagnetisation in a geo- 
metrical clamp with one of its poles close to the magnet of 
a magnetometer. 
The results obtained with the longitudinal detector in no 
less than 16 cases are identical with those found with the 
solenoidal one, showing that the demagnetisations of the 
core of the latter are not affected in the present instance 
by any vibration peculiar to the detector circuit. This — 
point has also been considered by Chant.’ The circuits. 
examined have been made of copper wire 0°33 cms. in 
1 Chant—Am. Journ, Sci., xv., p. 54, 1903. 
