ments. Perhaps I can best shew you what is required in the process of heating platinum by using that source of heat which we have here, and which seems to be almost illimitable—namely, the voltaic battery; for it is only in consequence of the heat that the voltaic battery affects the platinum. By applying the two extremities of the battery to this piece of platinum-wire, you will see what result we shall obtain. You perceive that we can take about this heating agent wherever we like, and deal with it as we please, limiting it in any way. I am obliged to deal carefully with it; but even that circumstance will have an interest for you in watching the experiment. Contact is now made. The electric current, when compressed into thin conducting-wires offering resistance, evolves heat to a large extent; and this is the power by which we work. You see the intense glow immediately imparted to the wire; and if I applied the heat continuously, the effect of the current would be to melt the wire. As soon as the contact is broken, the wire resumes its former appearance; and now that we make contact again, you perceive the glow as before. [The experiment
