86 Count Rumford’s Enquiry concerning the Nature of Heat, 
of an experiment, (which commonly lasted several hours,) that 
I was called away, and was not present to observe the thermo- 
meter, at the moment of the passage of the mercury through one 
or both of those points of its scale which formed the limits of 
the given interval, chosen as the standard for a comparison of 
the results of the experiments with each other, it became a 
matter of considerable importance, to find means for supplying 
these accidental defects, and ascertaining the points in question 
by interpolation. 
In order to facilitate the means of doing this, I endeavoured 
to investigate the law of the cooling of hot bodies in a cold 
fluid medium ; and I found reason to conclude. 
That if, on the right line AB, a perpendicular CQ be taken, 
equal to the difference of the temperatures of the hot body and 
of the colder medium, expressed in degrees of the thermometer; 
and, after a certain given time, represented by CE, taken on 
the line AB, at the point E, another perpendicular EF be 
erected, and EF be taken equal to the difference of the tempera- 
tures after the time represented by CE has elapsed ; and if the 
