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Lighting Buoys with Selenium Cells To the Editor of the SCIENTIFIC AMERICAN: It has just come to my notice the letter of Mr. A. K. Sloan in the June 7th issue of the magazine, on automatic lighting of light buoys by means of selenium cells, of which he suggests the use of the selenium cell to control the buoy. The controlling of buoys by the selenium cell is by no means new, as this has been manufactured by Ernst Ruhmer, and has been in operation on the Baltic Sea for many years. This has been described in Mr. William J. Hammer's book on selenium, etc., and also in a recent article on selenium by Dr. Hausmann in a recent issue of the SCIENTIFIC AMERICAN. It has been rumored that it might be adopted for use in the Panama Canal. I should think that Mr. Sloan is behind the times. SAMUEL WEIN. New York city. Raising a Wick Evenly To the Editor of the SCIENTIFIC AMERICAN: I attach hereon the drawing of an arrangement I have devised for raising the wick or wicks of an oil cook-stove straight. In the years during which I have used oil cookers, it has been my experience that after a short period the old-style ratchet spindle refuses to raise the wick evenly. One end is invariably raised higher than the other, and any pan or other kitchen utensil placed over the flame has its bottom covered with an extremely oily soot. To obviate this trouble I suggest the ratchet wheels be put on a double spindle; those near the front to be put on an outside or sleeve spindle, and the rear ratchet wheels being placed on a spindle running through the sleeveand extending the entire width of the wick tube. With this arrangement it is possible to raise one end of the wick independently of the other, thus adjusting the wick to give an even flame. REV. ALAN PRESSLEY WILSON. 1535 Edmondson Ave., Baltimore, Md. Price Maintenance and the Dealer To the Editor of the SCIENTIFIC AMERICAK We consider the action of some merchants (jobbers and retailers) in deliberately cutting the standard fixed prices on nationally distributed articles as absolutely unfair and unjust to the producers. It requires a long time and the expenditure of a great deal of money to establish a national demand for any manufactured product. And such demand can never be created or maintained except the product is of the highest merit. Instead of undermining the progress made by the producer through price cutting, the dealer should welcome an established, fixed selling price, alike to everyone, thereby assuring to himself a living margin of profit in handling such a product. I trust that through your campaign the public may come to view this proposition in its true and proper light. JOHN LTJCAS & Co., INC., ERNEST T. TRIGG, Vice-President and General Manager. Philadelphia, Pa. Our Poor Maps To the Editor of the SCIENTIFIC AMERICAN: What you have to say regarding map-making and publishing in this country is wofully true, and I have been swindled out of my money many times before I learned to look abroad for maps that are completely honest. Because it is not so much the fact that his maps are decades out of date that marks the American map-publisher as lacking in enterprise and self-respect, but it is the unreasonable dishonesty of palming off old maps for new that puts large publishers in a class with fake fire-sale merchants. I have often paid several dollars for a map bearing a recent date, to find it lacking in ten years old information, to find that the old date had been scratched off the plate and a new date fraudulently inserted. Think of such miserable tricks in the great and noble art of map-making! As I am on a geographical subject, I wish to point out a hoary, seemingly deathless inaccuracy, which crops out in the article Salving the 'Lutine.' The writer mentions The Barbadoes,whereas the correct name is Barbadospure and simple, being a single island of the West Indies, not a group of islands as many people seem to believe. MARION J. PORT. Los Angeles, Cal. Controlling the Mississippi With Small Dams To the Editor of the SCIENTIFIC AMERICAN: I have followed with great interest the articles which you have published concerning the recent floods in this section of the country. In all of the above I have not read of a single plan that looks practical or feasible. The method suggested to avoid future damage from great floods by building mighty dams and have great reservoirs impound the water does not seem wise or economical. It would require the condemnation of immense tracts of land that are too valuable to be used simply for the storage of waste water. Then, too, there would always be the danger of some of these dams bursting, and with the great amount of water back of them, would at various times do much damage in the valleys farther down. And this is the very danger we want to avoid. As our civilization progresses, and our farm lands become more and more improved, tiling is done and the water rushed into the streams and rivers, with the resultant flood. The National Government must interest itself in preserving the life and property of all the people, both up stream and down, and just how best to do this is one of the greatest conservation problems before it. As the reservoir plan is unsafe and undesirable, so, too, the suggestion that the country be reforested is untenable; it will never be done, it is too long a process, would require too great an outlay of public funds, and use up lands that cannot be spared. Then, too, the project of widening all the streams will not solve the problem, as that will only aid in carrying off water from one place to make it worse in another. There is a plan however that will do the business, and at no great expense; that will not cause a lot of the best land to become mere swampy, mosquito-breeding reservoirs. This plan is to have the Federal Government rent or buy the flood lands along all the upper streams, runs, creeks and rivers, and at appropriate places build small dams, with dikes and flood gates to hold back the water to a height of from five to ten feet. These dams can be made at a very small outlay as compared to the large dams for permanent reservoirs. Then, whenever there is a storm, let the gates be closed and catch the water in the basin thus formed until the dam overflows. After a week or two, one after another of the gates can be opened and allow the water to drain off. The holding back of the water in these small dams will cause a fertile deposit of sediment to be dropped on the flood land that will greatly improve it and not retard the farming interests in the least. A thousand such dams throughout Ohio during the recent floods would have saved many times their cost in life and treasure. The flood lands by this plan can be used every summer for raising crops, whether owned by the Government or individuals, and much of the poor, stony gravel patches found in bottom lands to-day, because of the rapid wash of streams, would disappear and become covered with the finest kind of soil. During the late flood the writer saw the rapid current of a stream--usually nearly a dry bed--wash away forty feet of the bank which had been under cultivation for years. The great damage was done when water backed up by a railway bridge broke loose, and all came down the stream at one time. This stream could easily have been controlled by dams as above described. By having small and numerous dams this danger of a great rush of water is remedied, for even if one or two should break down, it would have little effect, as there would be other reservoirs to catch and hold the surplus water. The writer claims for the small dams greater safety, economy in construction and maintenance, increased value in abutting property, and consequent increased production for the State, and less chance for graft in their construction. This last feature.might be objectionable to many of the Government experts, but it is worthy of consideration nevertheless. Fredericktown, Ohio. F. A. DAY, Ph.D.
