Dividing T1 by T, we obtain the ratio which the energy developed in heat
bears to the total energy of the blow.

With regard to the form of the zone of melting, it was found always to
extend round the edges of the indent produced in the bar by the blow. We
are speaking for the present of cases where the faces of the monkey and
anvil were sharp. On the sides of the bar the zone took the form of a
sort of cross with curved arms, the arms being thinner or thicker
according to the greater or less energy of the shock. These forms are
shown in Figs. 1 to 6. It will be seen that these zones correspond to
the zones of greatest sliding in the deformation of a bar forged with a
sharp edged hammer, showing in fact that it is the mechanical work done
in this sliding which is afterward transformed into heat.

[Illustration]

With regard to the ratio, above mentioned, between the heat developed
and the energy of the blow, it is very much greater than had been
expected when the other sources of loss were taken into consideration.
In some cases it reached 80 per cent., and in a table given the limits
vary for an iron bar between 68.4 per cent. with an energy of 40
kilogram-meters, and 83.6 per cent. with an energy of 90
kilogram-meters. With copper the energy is nearly constant at 70 per
cent. It will be seen that the proportion is less when the energy is
less, and it also diminishes with the section of the bar. This is no
doubt due to the fact that the heat is then conducted away more rapidly.
On the whole, the results are summed up by M. Tresca as follows:

(1) The development of heat depends on the form of the faces and the