76 Dr Stark on the Influence of Colour on Heat 



coloured parcels of wool, of which equal weights were taken, were 

 wrapped severally round the bulb of a delicate thermometer, 

 graduated on the tube ; the thermometer was then placed in a 

 glasstube,the tube plunged into boiling water, and the time which 

 elapsed during the rise of the thermometer from one given point 

 to another noted. The apparatus was in fact nearly the same 

 as that employed by Count Rumford. With twenty grains by 

 weight of each wool, the result was that. 



Black wool rose from 50" to 170° Fahr. in 6' 35" 



Green, . . . . . 7 43 



Scarlet, . . . . .83 



White, . . . . . 8 45 



The next set of experiments were made with the common 

 air thermometer, graduated to tenths of an inch in a descend- 

 ing series. The bulb was coated with the various colours as men- 

 tioned, and heat thrown on the ball by means of planished tin 

 reflectors about three inches in diameter, from a gas Argand 

 burner. At the commencement of the experiments the coloured 

 fluid always stood at 1°. Coated with blacking from a wax can- 

 dle, and the heat reflected as mentioned : — 



The fluid descended in a mean of four experiments to 83° 



Dark brown, a mean of three experiments to . 74 



Orange-red, ..... 58 



Yellow, .... . 53 



White, ...... 45 



Though the above experiments, and others detailed at length 

 in the paper alluded to *, particularly those with the coloured 

 wool, do not coincide exactly in minute particulars, the general 

 result of the whole is nearly the same as to the ratio of the ab- 

 sorbing powers. Minute difi^erences in experiments made at in- 

 tervals may be easily accounted for, from the various states of 

 aggregation of the wool, and its being placed equally, or not, all 

 round the bulb of the thermometer. The experiments with the air 

 thermometer are not liable to the same objection, and the mean 

 of a number of experiments made with this instrument would 

 afford a pretty correct estimate of the absorbent powers of diffe- 

 rent colours. 



The experiments decidedly shew that colour, independently 



• Phil. Trans. 1833. 



