500 Mr. J. E. Petavel. An Experimental 



Fig-. 13. — Showing that when a small mass of platinum (90 grammes) is used, the 

 light does not remain constant for any appreciable time. 





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JO 80 SO 40 50 60 70 80 



Time in Seconds. 



One of the determinations made with the aperture in the cover 2 -5 

 cm. in diameter, or nearly three times the area of the " normal " opening, 

 is illustrated in fig. 14 (see Table IX). The quantity of light differs 

 from the " normal " by less than 1 per cent. If the aperture in the 

 cover is increased much beyond this limit, or if the cover is removed 



Table IX. (See fig. 14.) 



With the Diameter of the Opening in the Cover of the Furnace 

 increased to 2*5 cm. 



Intensity of the Light from 1 sq. cm. of the Platinum at the 

 Temperature of Solidification = 1*005. 



Time. 1 



Photometer 

 reading." 2 



Light. 3 



10 



147 '8 



1-064 



20 



150 -0 



1-008 



30 



150 -7 



0-991 



40 



150-9 



0-986 



50 



151 '3 



0-976 



60 



152-0 



0-960 



70 



153-6 



-924 



80 



155-8 



-875 



90 



1 



160 -8 



0-776 



1 The time is counted from the instant at which the blow-pipe was stopped. 



2 The photometer reading is the distance in centimetres between the photometer 

 bea 1 and the incandescent lamp which served as a standard of reference. 



3 The unit of light is the mean of a number of determinations made under the 

 <: normal " conditions. 



