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BELL SYSTEM TECHNICAL JOURNAL 



of hydrogen or helium, according as they contain two neutrons and one 

 proton or two protons and one neutron. I now show pictures to 

 support these statements. 



In Fig. 6 the apparatus is shown in a sketch : the cloud-chamber or 

 expansion-chamber of C. T. R. Wilson, being the hollow cylinder which 

 is shown below in axial section, its top being a glass plate and its 

 bottom a piston-head which can be pulled very suddenly downward 



ONCOMING I 

 DEUTERONS 



k\\\\\\\\\\\H KVWWWWWH 



LAMP^ 



MICA WINDOWS 

 -SUPPORTED 

 ON GRID 



Fig. 6 — Expansion-chamber arranged for detecting transmutation by deuterons. 



by mechanism. Ordinarily the chamber is filled with moist but dust- 

 less air; when the piston-head suddenly drops, the air and the water- 

 vapor are sharply cooled by expansion, and the vapor condenses in 

 droplets upon whatever ions may be floating in it. The side-tube 

 which enters the chamber from above is evacuated; through it come 

 the impinging deuterons, to make their impacts upon the target at the 

 knob-like closed end of the tube. The wall of the tube, thin as it 

 may be made, is too thick to allow the deuterons to emerge into the 

 air of the chamber. One might well expect that a fortiori, any new 

 particles born out of the transmutation would be too slow-moving to 



