The hydraulic ram is another application of the same principle. Perhaps the reader may know some place where this apparatus can be used. Let us briefly describe the conditions of its operation. Near your house, at a lower elevation, may be a beautiful spring, so situated that, within the distance of about seventy feet, a fall of from five to ten feet can be obtained. Now run a large pipe from the spring to the spot where the ram is to be placed, below the level of the spring. The ram is a pear-shaped, cast iron cylinder, open at the small end, at which point a valve is placed, opening upward. The pipe coming from the spring is screwed into the bottom of the ram below this valve, in such a manner as to conduct the water past the valve, and out through an opening beyond. At this point, however, is placed a metallic valve, against which, as the water escapes, it continues to crowd. Presently the rushing stream obtains sufficient momentum to close this valve, and thus prevent for a moment its further escape. The accumulated force of the water then raises the valve in the bottom of the ram and it rises into the chamber, which is partially filled with air. This air is compressed, but on account of its elasticity at once reacts upon the water and forces it through another pipe to the required height. Only about one-eighth of the water is sent through the last pipe, as seven-eighths of it is required to force the remainder to the desired elevation. I have a great respect for this useful apparatus, the invention of the elder Montgolfier.[13] I know of one hydraulic ram which for fifteen years has raised, through a pipe twenty-two hundred feet long, to an elevation of seventy-five feet, an average of twenty-four barrels of water daily. Its total cost for repairs has not exceeded twenty-five dollars, and yet it has done every day the work of four men. If men had been hired to do this labor at $1.50 per day each, their wages would have amounted to the snug sum of $32,850. [Illustration: A FOUNTAIN MADE BY COMPRESSING AIR IN A BOTTLE.] Atmospheric pressure is employed in many of our cities to convey packages from one part of a building to another, and to even greater distances. This “Pneumatic Dispatch”[14] system, as it is called, was first tried successfully in Paris, in 1865. A company was then established, which now claims to send eight hundred and thirty packages daily. In our own country this curious appliance may be seen in operation at the United States Express office in New York City, in the mammoth establishment of Mr. Wanamaker, in Philadelphia, and doubtless in many other places. For many years attempts have been made to propel cars by compressed air, but as yet the expense of such a plan greatly exceeds that of steam. LIGHT.