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IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
property of unilateral conductivity to the same degree is also 
significant. 
Mr. Goddard 1 working with Tellurium- Aluminum contacts in 
vacuo, and in oxygen and air finds that such contacts possess 
unilateral conductivity in air and oxygen but not in vacuo. Mr. 
Goddard’s work and the behavior of zincite-copper contacts in 
vacuo and in hydrogen-sulphide constitute direct evidence that 
unilateral conductivity is a surface effect and that surface films 
of some sort are the seat of the action. 
It is possible that there are other gases capable of producing 
the same effect under proper conditions; some of the halogens 
for instance. However, no such compounds possessing rectifying 
properties, have been found in nature. 
Department of Physics, 
The State University. 
Physical Review, Vol. 34, p. 449. 
