On the Influence of Color and Radiation. 



23 



Second. — The correction for the altered circumstances of tempe- 

 rature of the room, &;c., may be tested by comparing the experiments 

 made with different cylinders having the same coatings on different 

 days. In the table on the preceding page, is given the various results 

 of this kind furnished throughout the series of experiments. The 

 date is given in the left hand column, and applies to all the results 

 on the same horizontal line with it. A comparison of the numbers 

 in the columns marked ratio, and on the same horizontal lines will 

 show how far the same reduction to a standard would have been giv- 

 en by different cylinders: in other words, how far the influence of 

 currents of air, local temperature, and radiation from or to adjacent 

 bodies might have interfered with the particular resluts. 



Of the ratios thus brought into comparison it will be found that in 

 one case the results are identical, in four others that they differ one 

 per cent., in two others two percent., in four others three, in one four, 

 in three five, in two seven, and in one ten percent : omitting this latter 

 the accordance is much less satisfactory than was shown by the form- 

 er table, and the average amount of error is nearly four per cent. 



Having now shown the probable hmits of accuracy in the experi- 

 ments, I proceed to compare together the reduced times of cooling 

 of the same cylinders with different coatings. In the table will be 

 given the observed time of cooling through forty degrees, and the time 

 of cooling of the standard, from whence the reduced times are dedu- 

 ced. As the colors of the substances were not in all cases what would 

 be expected, the color is designated in a separate column. 



Cylinder No. 1, variously coated. 



Nature of Coating. 



Carbonate of lead. 

 Vermilion. 



Golden Sulphuret of An- 

 timony. 



Red oxide of lead. 



do. additional coat. 



Do. blackened b}'- hydro 

 sulphate of potassa. 



Plumbago. 

 Gamboge. 



■^ C 



o 



Sees. 



864 

 806 



868.5 



890.5 

 932.7 



917.8 



787 

 808.7 



O !^ 



c a 



OT3 



Sees. 



1014 



937 



969 



948.2 

 950.2 



819.2 

 816. 



Pi 

 Sees. 



864 

 872 



909 



952 

 995 



966 



974 



1005 



Remarks. 



Smooth. 

 Smooth, with 

 minute cracks. 



Roughj peels 

 easily. 



Smooth. 

 For comparison 

 with following. 

 Red shows 

 through. 

 Uniform, but 



not glossy. 

 Smooth, but in 



streaks. 



