(18) T. W. asks: What size of breast water wheel, with a fall of 2 feet water, would it require to produce the same power as an overshot wheel of 4 feet diameter, 18 inches face, with a fall of 5 feet water? A. If the breast wheel gave the same efficiency as the other, it would require a face about 2½ times as wide.
(19) A. K. says: A. asserts that if a small and a large boiler be set side by side and connected with the top gauge cock of the two boilers, level, when they are first filled with water, and then steam is raised, that the water will not remain the same, that the pressure will be greater in the larger boiler, and consequently will force the water into the smaller one. B. says that the water will always remain the same as long as the boilers are connected; that the pressure on the water will be the same in both boilers, and therefore the water will always assume the same level in each. Which is right? A. The pressures sometimes vary in two boilers connected in this way; and they should be set in such a way that the water cannot be forced from one into the other under any circumstances.
(20) J. T. G. says: I notice your reply to W. G. in regard to pounding of a steam pump, in which you recommend the use of a larger air vessel. I think that W. G. can remedy the difficulty by allowing a small quantity of air to enter the pump cylinder at each stroke, which can be done without sensibly diminishing the amount of water delivered, provided the lift is not so high as to nearly equal the capacity of the pump. That would keep the maximum quantity of air in the air vessel, and I think that the air in the discharge pipe would have the effect of converting a comparatively rigid column into an elastic one. W. G. can easily try the experiment by running with the drain cocks at the end of his pump partially open; and if that remedies the difficulty, he might insert a small check valve opening inward to prevent the discharge of water during the out-stroke. If W. G. tries this, I wish that he would let us know the result through the SCIENTIFIC AMERICAN.
(21) G. H. says: Please decide the following: A. claims that a team of horses can draw a greater load when hitched close to it than when hitched at a distance of 10 or 20 feet. B. claims that, everything else being equal, distance makes no difference, and that the team could pull as many lbs. at a distance of 20 feet as it could at ten or less. Which is right? A. We incline to B.'s opinion.