84' Count Rumford’s Enquiry concerning the Nature of Heat , 
Though it was easy to discover, by a single glance at the re- 
gister, whether a covering which was put over one of the instru- 
ments prolonged the time of its cooling or not ; yet, in order 
to compare the results of different experiments, and particularly 
of such as were made on different days, so as to determine with 
precision how much warmer one kind of covering was than 
another, it was necessary to fix on some particular interval in 
the scale of the thermometer, or number of degrees, commencing 
at some certain invariable number of degrees above the tem- 
perature 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 instance,) in very nearly the same 
time, whatever was the temperature of the air of the room ; pro- 
vided always, that the point from which these 10 degrees com- 
menced, 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 experi- 
ments, is that which commences with th e fiftieth, and ends with 
the fortieth degree of Fahrenheit’s thermometer, above the tem- 
perature of the air in which the instrument is exposed to cool. 
When, for instance, the air was at 58°, the interval commenced 
at the 108th degree, and ended at the 98th. When the air was 
at 6 ^°, it commenced at 114^°, and ended at 104-i- 0 . 
That the same instrument, exposed to cool in the air, does in 
fact cool the same number of degrees in the same time, very 
nearly, when the given interval of the scale of the thermometer 
