An hydroelectro machine of the most extraordinary and unprecedented power is now being constructed for the United States. It will be able to produce a spark of 36 inches, to cost 3500 feet of metallic surface, in a battery of 48 Leyden jars, of two feet high by ten inches in diameter.

This shock would kill 1000 men in an instant, if it were passed through such a chain! This machine will be more than four times as powerful as one exhibited at the Polytechnical Institute, London, which is now by far the most powerful instrument in the world.

The expense will be 4500 dollars, with the apparatus for illustration. The name of this Leviathan machine is to be the "Benjamin Franklin;" and, as it will not be shown at all in Europe, America will possess exclusively this magnificent, unequalled instrument. It will leave manufactory for the United States early in the year.