30 Inquiry concerning the Nature of Heat, 



ter-sheets, and contains the results of an actual and very 

 interesting experiment, which lasted 26 hours. 



Though it was easy to discover, by a single glance at 

 the register, whether a covering which was put over 

 one of the instruments prolonged the time of its cool- 

 ing or not; yet, in order to compare the results of dif- 

 ferent experiments, and particularly of such as were 

 made on different days, so as to determine with pre- 

 cision how much warmer one kind of covering was than 

 another, it was necessary to fix on some particular in- 

 terval in the scale of the thermometer, or number of 

 degrees, commencing at some certain invariable number 

 of degrees above the temperature of the 'air by which 

 the instrument was surrounded, in order that the 

 warmth of the covering, or its power of confining heat, 

 might with certainty be estimated by the time employed 

 in cooling through that interval. 



By the results of a great number of experiments I 

 found that the same instrument cooled through any 

 given (small) number of degrees (10 degrees, for in- 

 stance) in very nearly the same time, whatever was the 

 temperature of the air of the room ; provided always, 

 that the point from which these 10 degrees commenced 

 was at the same given number of degrees above the 

 temperature of the air at the time being. 



The interval I chose for comparing the results of my 

 experiments is that which commences with the fiftieth, 

 and ends with the fortieth, degree of Fahrenheit's ther- 

 mometer above the temperature of the air in which the in- 

 strument is exposed to cool When, for instance, the air 

 was at 58, the interval commenced at the io8th degree, 

 and ended at the 98th. When the air was at 64^, it 

 commenced at 114^, and ended at 104!. 



