M. MELLONI ON THE POLARIZATION OF HEAT. 829 
with the amplitude of the primitive deviation, which we shall call the 
are of impulsion ; and we perceive that, the slowness of the motion at 
the extremity of this are enabling us to observe it with considerable 
exactness, it may be afterwards compared with the corresponding 
steady indication; which comparison may be easily extended to all 
points of the circuit if we vary the intensity of the calorific radiation by 
making the requisite change in the distance between the source and the 
pile. Moreover, the fixed deviations being given, the corresponding 
forces may always be determined by experiment*. We are therefore 
in possession of all the elements necessary for the construction of such 
a table as may immediately show the ratios of the forces according to 
the arcs of impulsion. The forces, as we know, represent the tempe- 
raturest : thus, by means of our table, the relative intensities of two ca- 
* For the description of the methods, see Bibliotheque Universelle, tom. lv. 
page9; and Mémaires de l’ Académie des Sciences, tom. xiv. p. 445 and 446. 
t M. Becquerel had shown in 1826 (Ann. de Chimie et de Physique, tom. 
XXxi. page 371) that the intensities of the thermoelectric currents of copper, 
platina, and other metals, are proportional to the temperatures through the 
whole extent of the thermometric scale. Now, the currents which produce the 
greatest possible deviation in the common thermomultipliers are derived from a 
heat, which scarcely rises to a few degrees, acting on one of their faces: the 
proportionality between the forces of magnetic deviation and the temperatures 
was therefore already established by experiment when I was commencing my 
inquiries into the nature of radiant heat. Hence it is that I have admitted 
that proportionality, as a known fact, in the preceding Memoirs on this subject. 
Nevertheless, as M. Becquerel had not operated directly on the metals which 
enter into the composition of the pile, the committee appointed by the Aca- 
demy of Sciences to examine my experiments on heat, manifested a desire that 
the proportionality of the forces to the temperatures in the thermomultiplier 
itself should be placed beyond the reach of doubt by some special experiments. 
With this view I procured a thermoelectric pile of four very minute elements (bis- 
muth and antimony) bent like a siphon, in order that each of the two termina- 
ting faces might be introduced into a separate recipient and different tempe- 
ratures imparted to them by the contact of heated liquids. The extremities of 
the two last elements stood out of the vessels into which the ends of the curved 
electric bundle had been plunged, and communicated with the galvanometer by 
two copper wires. But as a difference of some degrees was sufficient to drive 
the magnetic needles to the extremity of the scale, I placed in the electric 
circuit a very fine iron wire of several feet in length, The current then be- 
came so weak that a variation of a centigrade degree of temperature between 
the two faces produced in the galvanometer no more than a deviation of about 
one degree. Matters being now in this state, water more or less heated was 
successively introduced into one of the vessels and thawing ice into the other. 
The second face was thus kept constantly at zero, while the first tovk, in suc- 
cession, the different temperatures of the water, which were determined by a 
_ very delicate mercurial thermometer. The numbers of the degrees indicated 
by the thermometer plunged in the hot water were found exactly proportional 
to the corresponding electric forces or intensities indicated by the deviations of 
the galvanometer. The experiment was now varied in order to obtain a nearer 
_ approach to the circumstances in which the thermamultiplier is commonly em~ 
