336 Dulong and Petit onthe Measure of Temperatures, [May, 
and of the silvered thermometer, and the ratios between these 
velocities . 
Velocities of cooling Velocities of cool-| 
of the naked thermo-ing of the silvered) Ratios of thelerye- 
Excesses of temp. 
of thermometer. | | eter. shavasamier eet locities. . 
260° 24-42° 180" Fa 2°23" 
240 91-12 9-82 2-15 
220 17-92 8:59 2:09 
200 15°30 7:57 2:02 
180 13-04 6°57 1:98 
160 10-70 5°59 1-01 
140 8°75 4-61 1:89 
120 - 682 3°80 1-80 
400 5°56 3°06 1-81 
80 415 2°32 1°78 
60 2°86 1-60 1:79 
40 1-74 0:96 1-8] 
20 0:77 0°42 1:85 
10 0:37 019 | 1:90 
The mere inspection of the numbers inserted in the last column 
fully confirms the fact announced above. We perceive likewise 
the ratios of the velocities of the two thermometers remaining 
nearly the same for the excesses of temperature between 40° 
and 120°. This circumstance, resulting obviously from the 
ratios increasing, after having diminished, has probably contri- 
buted to persuade Mr. Dalton that the law of cooling in air 
must be the same for all bodies. If the above series were car- 
ried further, we should find that the ratio of the velocities of 
cooling which is already equal to 2:23 for an excess of tempera@ 
ture of 260°, inereases rapidly as that excess augments, and that 
it approaches more and more to the number 5:707 to which the 
- m=. - + . . 
fraction — is equal in the case of glass compared with silver. 
é 
We see from this to what a degree the consequences deduced. . 
by Mr Leslie, from experiments made at low temperatures, are 
inaccurate. For having imagined, as we have said im the 
beginning of this memoir, that the ratio which we have deter- 
mined above would continue always to diminish, he had supposed 
that it would terminate by becoming almost equal to unity ; so 
that at high temperatures, the total losses of heat would be | 
almost independent of the state of the surfaces. The laws 
which this philosopher has proposed, and likewise those of 
Dalton and Martie, may be all refuted by a single argument ; 
for all these laws make the velocity of cooling depend solely on 
the excess of the temperature of the body above that of the sur- . 
rounding medium; while experience proves that other things 
7 
