566 Dr. J. T. Bottomley on Radiation of 



Curves No. 1 and No. 2 were plotted from the results of 

 measurements of resistance and temperature made on the two 

 strips when dismounted after the radiation experiments. The 

 resistance numbers of Column 6 were then marked on these 

 curves, and the corresponding abscissae gave at once the 

 temperatures shown in Column 9. 



It will be seen by the divergence of Curves 1 and 2 that 

 the increase of resistance with temperature in the dull strip 

 is very slightly lower than that in the bright strip. This is 

 probably due to the conducting power of the thin filament of 

 lampblack which covered the strip. The lampblack would 

 have a slight effect in reducing the resistance of the strip, 

 and it would also have an effect, of minor order, in reducing 

 the rate of increase with temperature of resistance of the 

 coated strip. 



Curve 3 of the figure shows the watt-ratio for the two 

 strips at the mean of the temperatures given in Column 9. 



It appears from the table and the curves that the blackened 

 strip consumes energy at a greater rate than the bright strip 

 when the two are at the same temperature, and that at each 

 point when the strips are giving off an equal amount of light 

 the blackened strip is using much more energy per second 

 than the polished strip. 



It seems also that the ratio between the power used 

 by the two strips is much higher at the commencement 

 of luminescence than at a brighter heat ; and it may be 

 that a point would be reached at a very high temperature 

 where this ratio might become constant, or else that at an 

 extremely high temperature the power required to supply the 

 blackened and the bright strips might not be very different 

 in amount. 



The platinum strips were used in order to give a better 

 comparison by eye than can be got from thin wires of the 

 same electric carrying capacity, but it has been very difficult 

 to obtain platinum strips which would not break at a very 

 moderate temperature. I have tried commercial platinum 

 strip, and also strip of perfectly pure platinum ; latterly I 

 tried strip containing 10 per cent, of iridium in order to 

 harden it, but none has been as successful as I hoped. It 

 has been very disappointing that in every case one or other 

 of the strips broke, and my experiments have been stopped 

 before I could reach a really very high temperature. The 

 breaking of the strips is not to be attributed to an over great 

 tension in the spiral springs. The amount of pull in the 

 spiral springs was only so great as to take up the slack due 

 to the expansion of the platinum with heat. I have a very 



