A correspondent—Thomas H. Johns, of Point Worthington, Miss.—informs jus that egg-shaped water cisterns are becoming very general in the South and West, and that they are far superior to the flat-bottomed cisterns common at the East. The following is a description of the method of constructing the above-named cisterns :— "The ground is excavated to a greater depth at the center than at the sides, and rounded gradually towards the greatest width or circumference ; this forms the bed of an inverted arch. The bricks are laid in hydraulic cement, by commencing at the center, and when the arch bottom is formed, the side walls and top arch are constructed in the usual way." Our correspondent has had large cisterns of twenty feet diameter built in this manner, and he assures us they never fail when the workmanship is properly executed. Flat bottomed cisterns we know often leak, but this we have considered to be the fault of the workmanship. The masons do not generally make the bottoms of cisterns sufficiently thick, nor do they use a requisite amount of cement for the bed. As the egg-shaped cisterns have no jdge or angle at the bottom, of course they ire capable of withstanding a greater amount )f hydorstatic pressure than the flat bottoms, md are, therefore, not so liable to leak.
This article was originally published with the title "Egg-Shaped Cisterns" in Scientific American 13, 40, 318 (June 1858)