7 1% 
7 
M. Melloni on the Radiations of Incandescent Bodies, 
solve these different questions, of which some have been 
already studied by other philosophers, Professor Draper has made 
use of an instrument composed of a strip of platina ignited by 
the action of a voltaic current. The strip was vertical, its length 
one inch and one-third, its width the twentieth of an inch, and. 
its upper extremity being fastened to a firm support, it was kept 
stretched by a little weight furnished with a copper wire, that 
dipped into some mercury placed in a cup below. The electric cir- 
cuit was established by placing the mercury and the upper extrem- 
ity of the platina strip in communication with the poles of a Grove’s 
battery, of which the force, properly moderated by a Wheatstone’s 
rheostat, could be kept constant for about an hour. By means 0: 
this arrangement, the strip of platina, more or less ignited by the 
action of the voltaic current, preserved its rectilinear direction ; 
ping more or less deeply into the mercury. To determine the 
dilatations of the strip, there was attached to its free extremity a 
long and very slender horizontal lever, arranged in such a manner 
that the point of attachment was very near one of the extremities 
of the lever which worked upon a pivot, and the other end trav- 
ersed over a divided scale, taking a position more or less oblique 
to the horizon as the weight and wire descended by the dilatation 
of the strip, and indicating on the graduated arc the quantities 
sought. 
» The temperatures were then calculated on the hypothesis that 
they were proportional to the dilatation of the platinum; employ- 
ing for this purpose the coefficient of Dulong and Petit. It will 
be understood that these calculations are easily made when we 
know the length of the strip and of the lever, and also the posi- 
tion of their point of attachment. In the instrument employed 
b r, each degree on the graduated are a th to an 
elevation of sti I’. above the temperature of t 
uppose, now, we commence by using a feeble | current, the 
force of Siete is gradually increased by means of the rheostat. 
The heat correspondingly augments in the strip, and finally makes 
it visibly red hot in the dark room in which the experiment is to 
be conducted. The degree that the index marks is then to be 
in the dark for their eyes to acquire a due sensibility, ) and from 
_ the mean of all the observations the temperature at which the 
platina began to be red hot was calculated. From the expeximnsage 
our author this tomperaiiae is 977° F. 
determine whether all substances become red hot at the 
"which was closed, and placed in it Guccsinively : 
gas carbon, lead, weiner ther substan- 
