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MESSRS. EDITORS—Noticing your reply to R. D. C, of Mo., I send you the enclosed sketch of what I consider the best plan fox constructing a filtering cistern. Many (and in cities particularly) are dependent upon cisterns for their supply of water, and in times oi drouth the roofs become very dirty from dust and coal smoke, and unless the water is filtered, would be unfit to use ; but to filter it properly so as to remove every particle of dirt the water must percolate through the sand and gravel in drops. Now, in your small box arrangement, and a heavy dashing rain, a large amount of water is lost, or, if not, it h but little better for the filtering it has received, as it has passed through too rapidly. In the plan I propose, no w-ater is wasted, and the filtration is perfect; and, again, it has another advantage, it admits of the use of a cast iron force or lift pump in any weather, and ii generally adopted, there would be many more force pumps used than there are now, owing tc their liability to freeze, and become perfect nuisances in winter. S. II. HOLMES. Portsmouth, Ohio, Nov. 9, 1857. [We have engraved the drawing of our correspondent, and ife will be seen to be a very simple arrangement. A is the cistern, B a crown dividing it into two compartmcnts9 N the necks of the upper and lower crown ; on each side of the pump are square cast iron pans, C, with perforated bottoms, three or four of them being built in the lower crown, and their perforations to be covered with coarse flannel. D is an extra neck in the top crown to repair the pump or renew the filter. This filter can be used with a chain pump, by making a water tight box from the lower to the upper neck. It is a very good and simple contrivance, and we have no doubt that it will answer well.—EDS.
