Heat in the Spectrum. 115 



I have made use of four prisms : — (1) rock-salt, (2) flinti. 

 glass, (3) bisulphide of carbon, (4) quartz, cut out of the crystal 

 so as to give a single image. All the observations here recorded 

 were made on days when there was a cloudless sky. 



Table I. — Distribution of Heat by Rock-salt. 



Series I. Series 11. 



(1) Heat of the whole visible spectrum . 100 100 



(2) Heat of the more refrangible region .53 51 : 



(3) Heat of the less refrangible region . 47 49 * 



In this Table the column marked Series I. gives the mean of 

 four sets of measures, and that marked II. of three. At the 

 beginning of each set the rock-salt was repolished. 



Table II. — Distribution of Heat by FHnt-glass. 



Series I. Series 11. 



(1) Heat of the whole visible spectrum . 100 100 



(2) Heat of the more refrangible region .49 52 = 



(3) Heat of the less refrangible region . 51 48 



Series I. gives the mean of ten sets of measures, Series 11. of 

 eight. 



Table III. — Distribution of Heat by Bisulphide of Carbon. 



Series I. Series H; 



(1) Heat of the whole visible spectrum . 100 100 



(2) Heat of the more refrangible region . 52 49 



(3) Heat of the less refrangible region . 48 51 ; 



The sulphide employed was devoid of any yellowish tinge. It 

 was quite clear. Series I. is the mean of eight experiments, 

 Series II. of ten. 



Table IV. — Distribution of Heat by Quartz. 



Series I. Series II. 



(1) Heat of the whole visible spectrum . 100 100 



(2) Heat of the more refrangible region . 49 53 



(3) Heat of the less refrangible region . 51 47 



Series I. represents twenty-seven experiments. Series II. 

 twelve. In the former two quartz prisms were used to increase 

 the dispersion ; in the latter only one was employed. 



Perhaps it may not be unnecessary for me to say that I have 

 repeated these experiments many hundred times during a period 

 of several months, including the winter and the summer, vary- 

 ing the conditions as to the hour of the day, arrangement of the 

 apparatus, &c. as much as I could, and present the foregoing 

 Tables as fair examples of the results. Apprehending that the 



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