ON THE SEPARATION OF LIGHT AND HEAT. 127 



The lens, with its apparatus, was placed about three feet Portions of the 

 from the prifm; and, as the fun was pretty high in the greater pnfm. 



part of the experiments, and the defcending fpeclrum was in 

 general ufed, the floor under the (land, of the lens was in 

 (hade, from the wall below the window, and had been fo all 

 the day, as the window at which moft of the experiments were 

 made, fronted the fouth 



Some part of this detail might feem fuperfluous, had not 

 fuch ftrefs been laid on the fuppofed accumulation of heat in 9 



Dr. HerfchePs experiments, that it was necellary to obviate 

 any objection on that head ; or to (how, at leaft, the utter 

 improbability of any caufe of that nature having affected the 

 remits of thefe experiments. 



I now proceed to relate the experiments themfelves : which 

 I (hall tranferibe from the original notes made at the moment. 



April 6, 1801. 



The apparatus being difpofed as above defcribed, the co- Experiment r. 

 loured rays of the defcending fpe&rum of the prifm were f uc - Maximum riIe 

 cellively thrown on the flit in the fcreen, covering the lens ; f tne SJIJm' 6 

 and the thermometer with a blackened ball, placed in the fo- m blue = ** 

 cu$ of the lens, rofe as follows : ydlow rj 6 



In the blue in 3', from 55° to 56°. or 1 Q . red =r6 



Green in 3', from 54° to 58°. or 4°. beyond ^Js^ 



Yellow in 3', from 56° to 62°. or 6°. 



Full red in 2{% from 56° to 72*. or 16°. 



In the confines of the red in 2f, from 58° to 73£°. hr iSp. 



Quite out of vifible light in 2f, from 61° to 79°. or 18°. 



Between each of the obfervations the thermometer was 

 placed in the made fo long as to fink it below the heat to which 

 it had rifen in the preceding obfervation : of courfe its rife 

 above that point could only be the erTecl of the ray to which 

 it was now expofed *. A thermometer placed constantly in 

 the fhade near the apparatus, fcarcely varied during the expe- 

 riments. 



April 17th, 11, A.M. 



Three thermometers, ufed afterwards in the experiments, 

 were expofed to the fun's rays until they became flationary. 



* In all the experiments the thermometer was continued in the 

 focus long after it had ceafed to rife j therefore the heats given are 

 the greateft effect of the feveral rays on the thermometer in each ob- 

 fervation. 



The 



