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IOWA ACADEMY OF SCIENCE 
with each other. The arrangement of the crystals is probably irregular 
and complex. So it must be borne in mind that the experiments to be 
compared are not identical. There is only a general similarity, and the 
degree of likeness is not definitely known. 
THE VARIATION OF RESISTANCE WITH 'PRESSURE. 
That light-positive selenium changes its resistance to a remarkably 
large amount with pressure was accounted by the author some time ago 
(Phys, Rev. 20, 185, 1905, also paper by Brown and Stebbins, Phys. 
Rev. 26, 273, 1908). This large change may be produced by hydraulic 
pressure applied to the selenium between parallel wires less than one 
millimeter apart. The effect of pressure was studied more carefully by 
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