This is a useful machine, the principle of which is but partially understood and valued. To bring the hydraulic ram into operation, it is necessary that there should be a head or body of water, as a pond, supplied by a running stream, from which a fall can be obtained. The ram is an hydraulic machine composed of a body at the end of which is a valve called a pulse-valve, which is closed by the momentum of a running stream of water. On the top of the body is an air-vessel, in the neck of which is another valve which admits the water into the air-vessel upon the closing of the pulse-valve. The water meeting with an obstruction in the closing of the pulse-valve, immediately makes its way through the valve into the air-vessel. The air in the air-vessel becoming compressed, the valve leading into it closes, and thus liberates the pulse-valve. The same action takes place again with the pulse-valve, and also with the valve that leads to the air-vessel this continuous action takes place; and at each time a portion of water is forced into the air-vessel. When the air in the vessel is compressed so as to overcome the resistance in the pipe leading to the cistern, which it is intended to supply, the water flows over, and continues to do so, as long as the ram remains in action.

There is also a small valve in the neck of the air-vessel, introduced by Mongolfier's son, to supply the vessel with fresh air. Persons acquainted with hydraulics are aware that a column of water is equal to its base ; that is to say, a pipe resting on a base four inches square is equal to sixteen times, though it rested on an inch square. This is the principle of the ram, as the falling column, forcing up the pulse-valve, shuts it. Practice shows that a ten-feet fall will raise a column of water one hundred and fitly feet high, at the rate of five quarts per minute, or one part raised to eleven wasted, where the ram is only supplied by a two-inch pipe. I may further add, that theory teaches that a ten-feet fall will raise water three hundred feet high - of course, in a very small quantity. Mr. II. P. M'Birkin-brine, of Philadelphia, has been very successful in the construction of this valuable power.