JJ60 Iiifluence of Colour on tJie 



the change not only of its surface, but of a considerable part of 

 its mass, for the oil of lavender having evaporated, the hydro- 

 sulphate of potassa penetrated the coating. The substance by 

 means of which the coating was applied seems not to have sen- 

 sibly aitected the radiating power ; the carbonate of lead applied 

 with gum differing in radiating power but four per cent, from 

 that applied with oil of lavender. 



The colours rank from the foregoing table, blue, two varieties ; 

 black, brown, crimson, white, black, blue, white, three varieties. 

 There is no certainty that the litmus and alkanet, changed to 

 blue by potassa, were originally the same in colour. The sur- 

 faces were very different in regard to uniformity and smooth- 

 ness ; the alkanet was perfectly uniform, but not at all glisten- 

 ing ; it may be described as of a uniform minute roughness. In 

 this table, we have the greater number of whites at the bottom 

 of the scale of radiation, and of blue and black at the top ; but 

 this is all that can be said, for a white, a black, a blue, are in 

 close proximity near the middle of the scale. 



The results with the cylinders Nos. 4 and 5 were few in num- 

 ber. They are subjoined. 



Nature of Coating. 



Colour. 



Date. 



Observ- 

 ed time 

 of cool- 

 ing. 



Time of 

 cooling 

 of stand- 

 ards. 



Reduced 

 time of 

 cooling. 



Remarks. 



Ct/Knder, No. 4. 

 Cochineal. 

 Chromate of 7 



lead. 5 



Bi-sulphuret ^ 



of mercury V 



(vermilion). S 

 Sulphate of 1 



baryta. J 



IDitto. 



Cylinder, No. 5. 



^~-" n"* 



Bi-sulpliuret 

 of tin (au. 

 rum musi. 

 vum). 



eti 



Crimson. 

 YeUow. 



Red. 



White. 



Olive. 



Yellow. 



Nov. 1. 

 ... 6. 



...11. 



... 15. 

 ...21. 



Oct. 29. 

 ...31. 



Seconds. 



848.5 

 931.7 



843.7 



759.2 

 829 



845.5 



Seconds. 



894.5 

 948.5 



950.2 



865.2 

 861.7 



934 

 969 



Seconds. 



962 

 996 



888 



889 

 975 



917 

 1014 



Not uniform. 

 ( Very smooth 

 (and uniform. 



f Uniform and 

 ( smooth. 



Hough, 

 f Smooth, fresh- 

 < \y precipi- 

 ( tated. 



Smooth. 



Very even. 



The order from cylinder No. 4 is red, white, crimson, white, 

 yellow ; the influence of the roughness of surface is here plainly 



