(11) C. H. McK. asks: Would a pump so constructed as to create an incessant suction draw water an indefinite distance, or how far would it draw it? A. Such a pump would raise water no higher than any other that was equally tight. (12) J. W. says: I wish to get some boilers made about 12 inches in diameter and 13 inches deep. I want them to stand a pressure corresponding to 400° Fah°. Do you think it would be safe to have them made of cast iron? A. We think it will be better to use wrought iron. Make the shell about 7/16 of an inch thick. (13) J. R. S. says, in reply to E. W. P., who says that he has an artesian well which does not flow; but from which he pumps by inserting a pipe inside the well tubing, and asks: "If we attach the pump to the well tubing directly, allowing no air to enter the tube, would it not be like trying to pump water from an airtight barrel?" If such were the case, the drive well would be a miserable failure; for in all drive wells the pump is attached directly to the tube. I would advise E. W. P. to attach his pump to the well tube direct, and he will gain three times the amount of water that he now gets. By having his pump attached to the well tube directly, the working of the pump creates a vacuum, and the atmospheric pressure on the earth's surface violently forces the liquid to fill the vacuum thus formed, thereby giving a much greater amount of water than can be otherwise obtained. It is a well established fact that more water can be obtained by the drive well than by any other. A. In our answer to E. W. P., it will be evident, we think, to most of our readers, that we only referred to the case in which the well had no connection with the atmosphere, when the pipe was tightly fitted. It appears, however, that it might have been better to have stated this more definitely, and we gladly embrace the opportunity afforded by the interesting letters of our correspondents. We would be glad to receive from J. R. S. some experimental data in proof of his assertion as to the great gain from a tight connection. This also answers J. T. G. and W. H. F. (14) H. H. S. says: 1. Given, a boat with a 35 feet keel, of 6 feet beam, with fine lines; also a two-cylinder engine, each cylinder 4 x 5 inches; and a wheel 28 inches in diameter and of 3½ feet pitch. Will an upright boiler, with 135 square feet heating surface, and 4 square feet grate surface, be sufficient to run the engine at 250 or 300 revolutions per minute with 100 lbs. steam? A. With good coal and a forced draft, the boiler may be large enough. 2. What will be the probable speed of boat? A. In smooth water, 7 to 8 miles an hour. (15) F. A. asks: What would be a safe outside pressure for a cylinder of wrought iron, ½ inch thick and 4 feet in diameter, and 8 feet long? A. According to tables given in Wilson's "Treatise on Steam Boilers," the working pressure for such a tube would be about 65 lbs. per square inch.