A copper wire of length 1.317m and diameter 3.26 x 10^-4 m is blackened and placed along the axis of an evacuated glass tube.

The wire is connected to a battery, a rheostat, an ammeter, and a voltmeter, and the current is increased until, at the moment the wire is about to melt, the ammeter reads 12.8A and the voltmeter reads 20.2 V.

Assuming that all the energy supplied was radiated and that the radiation from the glass tube is negligible, calculate the melting temperature of copper.