234 
“3. The spark obtained when a capacity of .0005 to .012 M. F. and 
a self-induction of 0.0083 henrys has been introduced into the secondary 
circuit.” 
In this study it was found that ‘when the magnetic field was parallel 
to the spark length, the first type of spark presented two sheets of vapor 
in the form of spirals. In a field at right angles to the spark length this 
vapor is in the form of two semicircular sheets, one being on each side 
of the spark gap in a plane perpendicular to the direction of the magnetic 
field. 
“In the second type of spark (if the capacity did not exceed .002 M. F.) 
and in the third type brilliant spiral threads in a parallel field and bril- 
liant cireular threads in a transverse field took the place of the spiral and 
circular sheets respectively. In the first and second types of spark the 
bundle of threads across the gap could not be deflected by a magnetic 
field of 12,000 gausses. In the third type the metallic vapor and the 
threads across the gap were defiected in a very strong field and in a man- 
ner analogous to that of the circular and spiral threads. Reversing the 
direction of the magnetic field, or that of the current through the primary 
of the induction coil, changes the position of the sheets and of their ends. 
Decreasing the current through the primary or lengthening the spark gap 
sufficiently, causes one sheet or one set of threads to disappear.” 
The different parts of the deflected spark were analyzed by the spec- 
troscope, and it was found that the “Circular sheet of the first type of 
spark gave a spectrum of nitrogen bands, while the central threads 
showed that of the metallic lines and the air lines. The second type gave 
the same spectrum of bright air lines, and fainter metallic lines, for both 
circular threads and central threads. The third type showed the same 
spectrum (air lines) for ll metals used as electrodes. The spectrum of 
the circular threads showed the are lines in addition to the air lines.” 
By means of a rotating mirror, the velocity of the circular threads of 
the spark was determined, and from this a value for = calculated. 
Prof. A. L. Foley’ passed transversely through a long tube which 
served as a pinhole camera an electric discharge and observed that when 
a photographic plate was placed at the opposite end of the tube from the 
pinhole, the plate after exposure showed a shadow picture of a strean 
1 Not yet published. 
