‘ON THE INFLUENCE OF FRICTION UPON THERMO-ELECTRICITY. 103 
powers of the quantity that expresses the effect of contact. We have known 
from time immemorial that it developes heat, without understanding the 
reason of its so doing ; subsequently it was found that it developes the static 
electricity of isolators; and at length Mr. Faraday has found that it modifies 
equally the dynamic electricity produced by the contact of thermo-electrical 
conductors. In spite of the importance of this last fact and the weight of 
so great a name, it does not appear to have met with sufficient attention in 
scientific circles. Some observers, who appeal to the authority of Mr. Em- 
met, express what they consider to be the law of this action, by saying that 
thermo-electricity of contact is changed invariably into the opposite state by 
the friction of the two metallic factors. Others, on the contrary, deny in 
toto the influence of friction on thermo-electric phenomena. Thus it was 
recently adverted to in a scientific journal as a highly paradoxical fact, that 
in a given case the friction had caused a change of sign in the thermo-elec- 
tric declination produced by the contact of two heterogeneous metals; but 
at the same time this “ unheard-of” fact, as it was called, was explained by 
supposing gratuitously that the friction had been effected whilst keeping the 
metal to be rubbed in the naked hand, and in thus producing an accidental 
change of temperature. This explanation was offered on the assumption 
that friction in itself is not capable of producing any effect. Between the 
two extremes of tribothermo-eleetric omnipotence and nullity, I have tried to 
discover the middle course of truth. If Iam bold enough to call your atten- 
tion to some of the preliminary results of these labours, it is solely with a 
view of contributing to the more general discussion of this question, and 
with the hope of some observers joining me in these researches, and con- 
trolling, rectifying, and extending my experiments. 
For the experiments now to be mentioned, one of Nobili’s thermo-electric 
multiplicators of particularly delicate structure is requisite. Being furnished 
with an instrument of this kind, I proceeded in the following manner. A 
bar of bismuth was joined to that branch of the rheophore of this instru- 
ment where the silver of a voltaic element (silver and zinc) produces an 
eastern deviation, and a bar of antimony to the other branch of the rheo- 
phore. Both these bars were provided with handles, so that they could be 
employed without undergoing any change of temperature in the manipu- 
lation. When, through these being stationed in the same room, the two bars 
had previously arrived at the temperature of the surrounding space, no de- 
viation whatsoever was produced by their contact, but the slightest friction 
of either of them against the other gave immediately an eastern deviation. 
This latter extended even to an entire revolution of the needle in the same 
sense if the friction proceeded rather more rapidly. By gently raising the 
common temperature of the two bars to 30° or 35° of Reaum. scale, their 
contact in a state of repose always produced a stationary eastern deviation of 
about 30°, which by rubbing was further increased to 60°, and there likewise 
remained invariable as long as friction continued. At length, when I cooled 
the bars (below the temperature of the room) by the evaporation of naphtha 
vitrioli, their contact continually produced a western deviation, which by rub- 
bing was instantaneously changed into a contrary or eastern one of apparently 
the same amount as before, and this likewise remained stationary as long as 
the friction continued, but by the interruption of it the western deviation was 
immediately restored. This simple sketch of the phenomena of changes of 
intensity or even of sign, which friction at the point of contact gives to the 
deviation of a multiplicator’s needle, will already suffice to exhibit it as a mere 
consequence of the heat produced by the action of rubbing. Indeed, by 
joining to the point of contact of the two metals a button somewhat warmed 
