14-0 



the cylinder. Six of these instruments, with proper stands, and 

 auxiliary implements of obvious construction, were prepared for the 

 sake of comparative experiments. 



A previous trial was made with two of the cylinders, the vertical 

 polished sides of the one being naked, and those of the other covered 

 with one thickness of fine white Irish linen, strained over the metallic 

 surface. Here it was found, contrary to expectation, that in a cer- 

 tain space of time the covered cylinder had lost considerably more 

 heat than the naked one. 



In reflecting on this experiment it occurred to the author, that in 

 order to insure the accuracy of the comparison between experiments 

 made at different times and at different places, it would be necessary 

 to fix on some particular interval of the scale of the thermometer 

 above the temperature of the air by which the instrument is sur- 

 rounded. He therefore determined that all experiments should begin 

 at the temperature of 50, and end at 40 above that of the sur- 

 rounding atmosphere, an interval of 10 appearing to him sufficient 

 for the purpose of his investigation. Finding also that most experi- 

 ments would take up several hours, during which he could often not 

 be present to observe the thermometer at the different points which 

 ought to be ascertained, and observing that the rate of cooling of 

 hot bodies afforded a pretty regular progression, he determined to in- 

 vestigate this rate more minutely, with a view to obtain the means 

 of introducing such interpolations as would complete the series of 

 observations. Accordingly, on a given line, on which were set off 

 the times of cooling, he applied ordinates representing the different 

 temperatures corresponding to those times ; and having joined the 

 opposite terminations of these ordinates, he had the satisfaction to 

 find that this latter connecting line was in fact the logarithmic curve, 

 by means of which he would be enabled to supply by computation 

 any intermediate points which happened to have been neglected 

 during the observation. The problem according to which these in- 

 terpolations are to be computed, is given at full length. 



These previous precautions and expedients having been fully stated, 

 the author proceeds next to the .enumeration of his long series of ex- 

 periments, the first of which is merely the comparison, which has al- 

 ready been mentioned above, between the naked and the covered cy- 

 linders. The result was, that the former was 55' in cooling 10, 

 while the latter cooled through the same interval in 36% ; whence 

 it appears that clothing does in some instances expedite the passage 

 of heat out of a hot body instead of confining it. The only mode in 

 which it is thought that this unexpected result can be accounted for, 

 is by admitting that, as air is known to adhere with considerable 

 obstinacy to the surfaces of certain solid bodies, the particles of air 

 which were in immediate contact with the surface of the naked cy- 

 linder were so attached to the metal as to adhere to it with consi- 

 derable force ; and as confined air is known to be a very warm co- 

 vering, it seems probable that the retardation of the cooling in this 

 vessel was owing to that invisible covering, the air in contact with 



