652 



SCIENCE. 



[N. S. Vol. XX. No. 515. 



jfifty feet, J. J. Thomson found the positive 

 luminescence to travel in a direction opposite 

 that of the cathode particles in the Crookes 

 tube, with a velocity somewhat greater than 

 half the velocity of light. If this involved 

 an actual transfer of electrons by some hand 

 to hand process, it did not involve matter 

 which was concerned in producing spectrum 

 lines, since no Doppler effect is shown in the 

 positive luminescence (Spottiswoode and 

 Moulton). It might be suggested that the 

 positive luminescence was here produced by 

 cathode rays which found their way around 

 the bends of this long tube and finally struck 

 the anode, but this seems very improbable, 

 especially in view of the Wheatstone experi- 

 ment. 



It seems probable that the discharge from 

 a Ley den jar, or from a Holtz machine, differs 

 from that of a spark coil or from the current 

 originating in an armature of a dynamo. 

 If both positive and negative currents exist 

 in these last-named circuits, they are super- 

 posed in their origin, where the E.M.F. is 

 produced. In the Holtz machine, as in the 

 Leyden jar discharge, the positive and nega- 

 tive charges are separately accumulated, and 

 in this case the positive and negative currents 

 may perhaps be prevented from being super- 

 posed in the same discharge conductor. One 

 terminal of the machine or jar may be con- 

 nected to a large many-pointed conductor, 

 suspended in the outer air on silk fibers. 

 That terminal of the machine is then grounded 

 on the dust particles in the air. The other 

 terminal may be grounded either in a like 

 manner, or on the gas pipe. Wheatstone gaps 

 may be made in either of these circuits of 

 unipolar discharge. These gaps may be either 

 in open air or in tubes having any degree of 

 exhaustion. Wheatstone's experiment under 

 these conditions is likely to tell us something 

 about the motion of positive and negative 

 electricity in a conductor. 



It is interesting to observe here that a 

 Crookes tube will operate well in either of 

 these unipolar circuits. The same exposure 

 to the X-ray will give pictures of equal density 

 when developed together in the same bath. 

 In one case, however, the cathode terminal is 



connected to the negative terminal of the 

 machine. In the other circuit, it is connected 

 to the air contact, and is acted upon only 

 inductively by the anti-cathode which is con- 

 nected to the positive terminal of the machine. 

 In the first case the cathode discharge appears 

 normal and stable. In the second case, it 

 seems unsteady, it is greatly affected by the 

 motion of surrounding bodies, and it can be 

 suppressed entirely by bringing the open 

 hands near the tube so as to partly enclose it. 



The pointed air terminal may be replaced 

 by a flaming gas torch made of gas-piping 

 closed at its upper end and having many 

 small perforations, the lower end being con- 

 nected with the gas main by rubber and glass 

 tubing, the latter being kept dry by heating. 

 The carbon particles then serve as the carriers. 

 An insulated water tank in open air, from 

 which the water escapes in a fine spray, is also 

 effective. 



If what we call the free charges on the 

 terminals of the machine are delivered to the 

 small particles which float off into the air, it 

 would seem that in these unipolar discharges 

 we may find that even if positive and negative 

 currents are superposed they may not be equal 

 in value. For certainly in both circuits the 

 dominating action comes from the machine. 

 Francis E. Nipher. 



SCIENTIFIC NOTES AND NEWS. 



Professor Simon Newcomb has been elected 

 a corresponding member of the Vienna Acad- 

 emy of Sciences. 



It is reported that the Nobel prize for medi- 

 cine will this year be awarded to Dr. Robert 

 Koch. 



Professor William T. Sedgwick, head of 

 the biological department of the Massachusetts 

 Institute of Technology, has been elected an 

 honorary member of the New England Water 

 Works Association. 



Professor Martens, director of the Insti- 

 tute for Testing Materials at Berlin, has been 

 elected a member of the Berlin Academy of 

 Sciences. 



Professors Paul Mansion, professor of 

 mathematics, at the University of Genth, M. 



