3. _Heat a Degraded Form of Energy._—We have seen that thermal energy is not directly transformed into chemical energy. There is yet another restriction in the case of this thermal energy if we study the laws which govern the circulation and the transformations of thermal energy; and the most important comes from the impossibility of transporting it from a body at a lower temperature to a body at a higher temperature. On the whole, and because of these restrictions, thermal energy is an imperfect variety of universal energy, or, as the English physicists call it, a degraded form. 4. _Simple Transformations of Electrical Energy. Its Intermediary Rôle._—On the other hand, electrical energy represents a perfected and infinitely advantageous form of this same universal energy, and this explains the vast development of its industrial applications within less than a century. It is not that it is better known than the others in its nature and in the secret of its action. On the contrary, there is more dispute than ever as to its nature. To some, electricity, which is transported and propagated with the speed of light, is a real flux of the ether as was taught by Father Secchi, who compared it to a current of water in a pipe. It would do its work, just as the water of the mill does its work by flowing over a wheel or through a turbine. Electricity, like water in this case, would not be an energy in itself, but a means of transporting energy. To others, such as Clausius, Hertz, and Maxwell, it is not so; the electric current is not a transport of energy. It is a state of the ether of a peculiar, specific kind, periodically produced (electric oscillation), and propagated with a speed of the order of that of light. However that may be, what constitutes the essential peculiarity of electrical energy, and what causes its value, is that it is an incomparable agent of transformation. Every known form of energy may be converted into it, and inversely, electrical energy may be changed with the utmost facility into all other energies. This extreme adaptability assigns to it the part of an intermediary between the other less tractable agents. Mechanical energy, for instance, lends itself with difficulty to the production of light, that is to say, to a metamorphosis into photic energy (a variety of thermal energy). A fall of water cannot be directly utilized for lighting purposes. The mechanical work of this fall, which cannot be exploited in its present form, serves to set in motion in industrial lighting the installations, the electric machines, and the dynamos which feed the incandescent lamps. Mechanical work is changed into electrical energy, and it, in its turn, into thermal or photic energy. Electricity has here played the part of a useful intermediary.