Radiation of Non-Liiminoiis Heat, 257 



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

 perature of the room, &c. may be tested by comparing the expe- 

 riments 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 resuhs on the same horizontal line with it. A 

 comparison of the numbers in the columns marked ratio, and on 

 the same horizontal lines, will shew how far the same reduction 

 to a standard would have been given by different cylinders : in 

 other words, how far the influence of currents of air, local tem- 

 perature, and radiation from or to adjacent bodies, might have 

 interfered with the particular results. 



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 per cent. ; in four others 

 three ; in one four ; in three five ; in two seven ; and in one ten 

 per cent. ; omitting this latter, the accordance is much less satis- 

 factory than was shewn by the former table, and the average 

 amount of error is nearly four per cent. 



Having now shewn the probable limits of accuracy in the ex- 

 periments, 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 deduced. As the colours of the substances 

 were not in all cases what would be expected, the colour is de- 

 signated in a separate column. 



Cylinder J No. 1, variously coated. 



Nature of Coating. 



Carbonate of I 

 lead. / 



Vermilion. 



Golden sul- \ 

 phuret of V 

 antimony, j 



Red oxide of ) 

 lead, f 



Colour. 



White. 



Red. 



Brown 

 nearly 

 black, 



Orange. 



\] 



Date. 



Oct. 24. 

 25. 



31. 



Nov. 6. 



Observ- 

 ed time 

 of cool- 

 ing. 



Seconds. 

 864 



868.5 

 890.5 



Time of .Reduced 



cooling 

 of stand- 

 ard. 



Time of 

 cooling. 



Seconds. Seconds. 

 1014 864 



937 



969 

 948.2 



872 



909 

 952 



Remarks. 



Smooth. 



Smooth, with 

 minute cracks. 



Rough, peels 

 easily. 



Smooth. 



