688 
Transactions of the Royal Society of South Africa. 
For fig. 2 the resistances consisted of spiral wires of No. 22 S.W.G-. 
thickness (0-71 mm.), wound on mandrils | in. thick, and freely suspended 
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between the ends, giving excellent ventilation. We see that with an increase 
in the temperature the emission of heat improves, dropping from 150 at 
