The Story of Electricity

k showed that heat might take the place of chemical action. Thus, if a bar of antimony A (fig. 22) and a bar of bismuth S are in contact at one end, and the junction is heated by a spirit lamp to

without the couple shows that the bismuth is positive to the antimony. This property of generating a current of electricity by contact under the influence of heat is not confined to bismuth and antimony, or even to the metals, but is common to all dissimilar substances in their degree. In the following list of bodies each is positive to those beneath it, ne

SI

sm

ba

ass

ck

di

e

i

pp

at

lv

i

dm

se

r

phos

ti

lur

le

GA

of electricity. Within certain limits the current is, in fact, proportional to this difference of temperature. It alw

negative pole of the next. Now, if all the junctions on the left are hot and those on the right are cool, we will get the united effect of the whole, and the total current will flow through the wire W, joining the extreme bars or positive and negative poles of the battery. It must be borne in mind that although the bismuth and antimony of thi

leaner and less troublesome than the chemical battery, for it is only necessary to keep at the required difference of temperature between the hot and cold junctions in order to get a steady current. N

ne and iron for the other. Prisms of the alloy are cast on strips of iron to form the junctions. They are bent in rings, the junctions in a series making a zig-zag round the circle. The rings are built one over the other in a cylinder of

a delicate detector of heat by virtue of the current set up, which can be measured with a galvanometer or current meter. Piles of antimony and

phs, and they are capable of supplying small installations of

couple from the antimony to the bismuth we shall find the junction cooled. This "Peltier effect," as it is t

than another. Thus a sensitive galvanometer will show a weak current if a copper wire connected in circuit with it be warmed at one point. Moreover, it has been found by Lord Kelvi