All reference to back numbers sho'uld be b/.j volume and page. E. N. B., of Ottawa, Ca.—)[o method of trisecting an angle based upon principles of plane geometry bas ever been discovered, though many attempts have been made. Believing the problem impossible. the prizes offered at one time by several learned societies for its solution have all been officially withdrawn, notwithstanding ambitious geometers arestill busying themselves with the problem. An attempt at its solution, recently made by Patricio M.Del, Rio, ex-prjfessor in tlie Peruvian Naval Academy, has been reccotly published, but it has since proved to be erroneous. You will find immortal fame sooner in other pursuits than in muddling- your brains with thisquestion. J. M., of S. C.—No simple rule has eveCl,been found for determining the size of a second pulley, only the distance between centers, length of belt, and diameter of first pulley being given. A solution has, however, been sought by eminent mathematicians. The problem is extremely difficult, and involves the higher mathematics for even an approximate solution. The practical and proper way to workis to f x the size ofbotli pulleys and determine the length of belt accordingly; and actual measurement is the readiest way to determine the length of a belt when the diameter of the pulleys in which it is to run are given. J. W. M., of Ind.—The best,,varnish we know for the preservation of a portable boiler liablc to rust through exposure to out-door influences is asphaltum. This substance readiiy dissoives in turpentine. which forms a good vehicle for its application. We presume you can ob - tain it ready mixed. J. W. M., ofPa.—Nails are made of any size ordered, provided the order is large enough. We do not know whether the size you mention is kept on hand or not by any dealers, but are inclined to think it is not. VV. B. L., of Vt.—There is no cheap metal that will withstand the action of salt water. You can obtain all kinds of rubber tubing any dealer in rubber goods. R A. C., of Ky.—You can render brittle sheet brass tough by annealing, that is, heating it and plunging it in cold water. G. S. R, of Mass.—There is no gain in using high steam for heating purposes. The total amount of heat in stsam at any pressure is found by adding the latent her.t to tlie sensible heat or temperature, and this is practically a constant sum for all pressures.