- 
248 Dulong and Petit on the Measure of Temperatures, [Arrit, 
A series so extensive as the preceding is sufficient to prove 
that the formula which applies to the cooling of the glass bulb 
in vacuo extends likewise to the case of the silver bulb, preserv- 
ing to a the same value. However, not to neglect any of the 
means of verification in our power, we altered the temperature of 
the surrounding medium, and raised it to 80°. The preceding 
coefficient of (a' — 1) must be multiplied by a®; which gives 
V = 0°658 (at — 1) 
Excesses of temp. or Values of V ob- Values of V cal- 
values of ¢, served. culated. 
PAP oo eieare'e pietababetats AS “dha aig ais 'vlslatatite 3°44° 
> og Mee tate . 2:86 
NE AL a iat POE RIS 2:37 
180 | erat RRR eee 1:94 
BR leas Ay shin vin eae Trea fait ‘as pia k ele 1-58 
Bae ine 6 kGrofe nip ean DE ir ot Vial 3 Goal nd 1-26 
‘ro, RRO nae esat¥he > Abtiaat ets nusbhed ele wis dak 0-98 
Mg SARs > RSE A HE 0:76 
ed cask, settle he td UDO. coiid o nla ee | 
The simplicity and generality of the law which we have just 
established, the precision with which it is confirmed by obser- 
vation through an extent of nearly 300° of the thermometric 
seale, show clearly that it will represent rigidly the rate of 
cooling in vacuo at all temperatures and for all bodies. 
Let us now return to the calculation which led us to the dis- 
covery of this law. 
The total radiation of the surrounding medium is represented 
in it by F (6), and we find for its value, 
m a? + a constant quantity. 
But the point of commencement from which the absolute 
temperatures @ are reckoned being arbitrary, we may choose it 
in such a way that the constant quantity shall be null; which 
will reduce the expression to m a’. We may conclude then that 
if it were possible to observe the absolute cooling of a body in a 
vacuum ; that is to say, the loss of heat by the body, without 
any restoration on the part of the surrounding bodies, this cool- 
ing would follow a law in which the velocities would increase in 
a geometrical progression, while the temperatures increase in an 
arithmetical progression; and further, that the ratio of this 
geometrical progression would be the same for all bodies, what- 
ever the state of their surfaces may be. 
From this law, very simple in itself, is deduced as a conse- 
quence, that of the real cooling of bodies in vacuo; a law which 
we have already announced above. In fact, to pass from the 
first case to this, it is only necessary to take into the account 
the ny. of heat sent back every instant by the surrounding 
medium. This quantity will be constant, if the temperature of 
the surrounding medium does not vary: Hence it follows, that 
a 
