316 Prof. R. W. Wood on th 



ic 



agreement with the fact that the magnetic ray curves toward 

 an auxiliary magnet when the two nearest poles of it and 

 the field magnet are unlike in sign, and is repelled when 

 these poles are of like sign. Now, the magnetic field in 

 these experiments is produced by a magnet placed at one 

 end of the tube and the magnetic lines of force diverge in 

 the tube. The fall of magnetic potential is also least rapid 

 along the lines which lie near the axis of the tube. It would 

 seem as if the magnetic rays, when the auxiliary magnet is 

 not used, should be a diverging cone of light. Yet the most 

 noticeable action of the magnetic field is to condense the 

 light near the axis of the tube. And the stronger the field 

 is made, the more sharply converging the cone of light 

 becomes and the more contracted to the axial part of the 

 tube. 



These experiments should not be regarded as other 

 than very incomplete, since the phenomena appear to be 

 quite complicated. The attempt is being made to increase 

 the discharge without unduly increasing the potential and 

 to study the action of other gases and the state of the gas in 

 different parts of the tube. 



UniYersity of Cincinnati, 

 April, 1912. 



XXVII. Preliminary Note on the Electroii Atmospheres of 

 Metals. By R. W. Wood, Professor of Experimental 

 Physics, Johns Hopkins University, and Adams Research 

 Fellow of Columbia University *. 



THERE has been a good deal of controversy recently as to 

 whether air at atmospheric pressure will carry a current 

 of electricity, when the potential between the electrodes is 

 less than what is known as the critical potential (something- 

 over 300 volts). Earhart, in a paper published in 1901 (Phil. 

 Mag. [6] i. p. 147), described experiments which appeared 

 to show that a discharge might occur with as low a potential 

 as 32 volts, the gap between the electrodes being of the 

 order of magnitude of the wave-length of light. This result 

 was called into question by Almy, who worked with very 

 small platinum beads as electrodes, and failed to obtain any 

 evidence of discharge at voltages below 300. During the 

 progress of the work about to be described a paper appeared 

 in the Phil. Mag. by Anderson and Morrison (May 1912) 

 which gives further evidence that currents may flow across 



* Communicated by the Author. 



