OF ARTS AND SCIENCES. 161 



Experiments with Black Oxide of Iron (Fe 3 4 ). 



The wire was next coated with the black oxide of iron, which, 

 though resembling in color the oxide of copper, is very different from 

 it in chemical composition. 



A solution of sulphate was applied with a brush, the volatile 

 products being driven off by heating, and a coating of the Fe 3 4 

 formed. 



It was found that the form of the curve did not appear to vary 

 with the temperature, and the mean of four careful series is given in 

 Plate IV. and Table III., together with the probable error of deter- 

 mination of a point at the B line. 



Experiments with Green Oxide of Chromium (Cr 2 3 ). 



The green oxide of chromium was prepared by coating the wire 

 with chromic acid, and heating ; the water was thus driven off and the 

 higher oxides formed. 



The resultant curve is shown in Plate IV. and in the accompanying 

 table. 



Experiments with White Oxide of Aluminium (A1 2 3 ). 



The wire was coated by applying a solution of ammonia alum, 

 which, upon heating, was changed to A1 2 3 , the other products being 

 volatile. The substance thus formed was hard, vitreous, and pure 

 white. 



Nine series of experiments were made at several different tempera- 

 tures to see that the form of the curve was the same. The mean 

 result is given in Table III. and Plate IV. 



It now remains to see what conclusions may be drawn from a study 

 of these curves, and a comparison of them with each other. 



The curves for platinum show very plainly, and those for the other 

 substances confirm the conclusion, that the geometrical form is nearly 

 independent of the temperature. 



The study of the radiation from copper oxide enables us to extend 

 this conclusion to the liquid state, so that we may conclude in general 

 that the distribution of heat in the spectrum of a solid or liquid source 

 of radiation is nearly independent of the temperature of the source. 



Of course this conclusion can only be accepted within the limits 

 that the accuracy of the experiments prescribes, and it must be 

 admitted that further researches of greater delicacy may reveal slight 

 variations in the form of the curve. 

 vol. xiv. (n. s. vi.) 11 



