322 IOWA ACADEMY OF SCIENCE 
Apparatus, and Experimental Methods . — ^We were supplied 
with a series of wires of phosphor bronze, all drawn from the 
same original alloy. There were thirteen of these wires, repre- 
senting successive drawings, and ranging in diameter from .100 
mm. to .508 mm. Previous work by one of us, already referred 
to, indicated that platinum iridium wires showed a marked devi- 
ation from constancy of period with varying amplitude, the 
larger periods being associated with the larger amplitudes, and 
particularly it was pointed out that the variation became more 
