636 Prof. Pollock: Comparison of Periods of 
the experimental evidence, that there can no longer be any 
doubt that the wave-length of the free oscillation associated 
with open circuits is considerably greater than twice the 
length of the wire. 
General Results. 
Open Circuits —A. Slaby (Electrotech. Zeit. No. 9, p. 165, 
1902) has investigated with a spark-micrometer the potential 
at various points of a straight wire when electrical vibrations 
take place along it. He finds a stationary wave with 
potential loops at the ends, and a relative node at the middle. 
Such an experiment does not seem calculated to determine 
the actual wave-length of the vibration connected with the 
wire, but apparently Dr. Slaby is satisfied, from a consi- 
deration of the observations, that the wave-length of the 
oscillation is equal to twice the length of the wire. He has 
also theoretically discussed the problem, and “ the calculation 
gives a full confirmation of the experimental results.” The 
experiments were made with wires from one to ten metres 
long. 
Drude, in Ann. der Phys. ix. 2, p. 293 (1902), publishes an 
account ofan elaborate research on the vibration-period and 
self-induction of wire coils, in connexion with the construction 
of Tesla transformers. On page 328 he gives the results of 
the investigation with coils with few windings and with 
single circles. Drude does not measure the period of the 
vibration connected with straight wires, but states that for a 
thin straight wire the half wave-length is equal to the length 
of the wire. He refers to a calculation of Abraham ( Wied. 
Ann. vol. Ixvi. p. 471, 1898) which gives the half wave- 
length 0°85 per cent. greater than the wire-length, for a 
straight wire 0°25 em. in diameter and 77 ems. long. 
In the present experiments, the comparison of the periods 
has been made in all cases between circuits constructed of 
copper wire 0°33 cm. in diameter and rectangles of thin 
brass wire 0°04 cm. thick, the rectangles being 30 ems. 
wide. 
It is found that the perimeters of the rectangles are greater 
than twice the length of straight wires which have the same 
period of electrical vibration, the ratio of the lengths varying 
from 2°45 for a rectangle 760 cms. in perimeter, to 2°31 for 
one whose perimeter is 1200 ems. 
Approximately at least, the wave-length of the electrical 
vibration associated with narrow rectangular closed circuits 
may be taken as equal to the perimeters of the rectangles. 
It appears then from these experiments, that the wave-length 
