Peltier's numerous papers are devoted in great part to atmospheric electricity, waterspouts, cyanometry and polarization of sky-light, the temperature of water in the spheroidal state, and the boiling-point at high elevations.

His name will always be associated with the thermal effects at junctions in a voltaic circuit,[4] a discovery of importance comparable with those of Seebeck and Cumming.

[5] Peltier discovered the calorific effect of electric current passing through the junction of two different metals.

The Peltier effect is the presence of heating or cooling at an electrified junction of two different conductors (1834).

This reversible effect is proportional directly to the strength of the current, not to its square, as is the irreversible generation of heat due to resistance in all parts of the circuit.

It is found that, if a current pass from an external source through a circuit of two metals, it cools one junction and heats the other.

[9] Typically, the use of the Peltier effect as a heat pump device involves multiple junctions in series, through which a current is driven.

The true importance of this "Peltier effect" in the explanation of thermoelectric currents was first clearly pointed out by James Prescott Joule; and Sir William Thomson[14] further extended the subject by showing, both theoretically and experimentally, that there is something closely analogous to the Peltier effect when the heterogeneity is due, not to difference of quality of matter, but to difference of temperature in contiguous portions of the same material.

Shortly after Peltier's discovery was published, Lenz used the effect to freeze small quantities of water by the cold developed in a bismuth-antimony junction when a voltaic current was passed through the metals in the order named.