234 



"3. The spark obtained when a capacity of .0005 to .012 M. F. and 

 a self-induction of 0.003 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 circular 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 deflected 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 all metals used as electrodes. The spectrum of 

 the circular threads showed the arc 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. 



M 

 Prof. A. L. Foley 1 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 stream 



1 Not yet published. 



