Proposed Industrial Fair at Washington. MESSES. EDITORS:—There is now in the Treasury of the United States more than $500,000 of money received through, the Patent Office in excess of expenses. The average amount of such,surplus that may be calculated .upon hereafter will not be less than $200,000 per annum. All the other bureaus are maintained entirely at the expense of the Treasury. But Congress intended that the Patent Office should be in the main self-sustaining, and to the special tax necessary for that purpose the inventors of the world—for whose benefit the Office was created—consent. It seems reasonable, however, that the taxes thus paid by them should be appropriated for their benefit, and that they should not be diverted to other uses, so long at least as there were wants of their own to the relief of which the money might properly be applied. Now the models which are required by law are of great and daily importance, and should not be dispensed with an-.j less from necessity. But tha space provided for them is al-'j ready mainly occupied, and about 5,000 square feet of additional shelf surface is required every year. It would also be of great advantage to the supporters of the Patent Office if opportunity were afforded to exhibit working machinery as well as manufactures and other products. Two years ago it occurred to m that this surplus, which was then said to be of about half its present amount, might with propriety and advantage be applied to the commencement of a structure that would moet present wants and be capable of indefinite expansion. An eminent architect expressed the opinion that such an undertaking would be perfectly feasible. It was believed that from moderate beginnings the present wants of the Office and its patrons might thus be supplied by an institution that would grow into proportions commensurate with the growing requirements and capabilities of the American people, that international rivalries might also be invited—that it might thus at length become developed into a permanent world's fair, at the same time that it subserved the legitimate purposes of the Patent Office. Circumstances prevented an effort to carry out that project then, but other circumstances have revived the intention now. At least it has seemed proper that the idea should be presented and discussed, and, if deemed expedient, adopted and urged to its consummation. An effort is now being made by the people of this district to hold a World's Pair in this city at no distant day. Nearly half a million of dollars have already been subscribed for that purpose, and it is confidently believed that this amount may be increased to 1,000,000. Especially if, instead of being a temporary undertaking, it is made one which contemplates permanency. Now if "these two projects were united, could they not be worked up into what might prove a great mutual as well as general advantage 1 There is competent authority for saying that with $1,500,000 a permanent structure of iron and glass might be made of a capacity at least equal to that of the entire Patent Office building. Sufficient space for the arrangement and pres?rvation of models would thus be provided as well as for manufactures and machinery of all descriptions. A permanent temple would thus be erected to human ingenuity to which men of genius from all quarters would resort to give and receive new inspiration. I hope the thought will not be deemed extravagant that under the united influence of the Smithsonian Institution, the Patent Office, and the Agricultural Department, this establishment might at length become the chief center of the arts and sciences of the civilized world. As far as has been yet ascertained the matter as thus presented meets with favor among those under whose auspices the project of a World's Fair here has been inaugurated. Before making any serious effort on the subject, however, it is thought expedient to know the views of inventors and their friends on this subject. Your position and character render your opinions of great moment, and on that account I now address you. ' It is not proposed to ask the appropriation of a single dollar by Congress. All that would be expected from that quarter would be a permission to appropriate funds which rightfully belong to the Patent Office to aid in carrying out the common enterprise which is mainly for its benefit. I am fully conscious of the fact that, in a mere financial point of view, the " Exposition " would prove a much greater success, if held in some large commercial city. But that is not the question now. The enterprise is already undertaken. It will be carried through, as I am assured. Whether it prove a financial success, or otherwise, to the stockholders is not an element in our present calculation. It is only her -that the Patent Office could, with any propriety, connect itself with such an undertaking, for it is only here that this undertaking could yield those advantages that would justify the connection and expenditure. Besides, Washington is not the commercial rival of any other city, and the jealousy that might be excited against most other plans of like magnitude would interpose no obstacle here. Washington. D. C. CHAS. MASON. Magnetic Action of Wind Currents. MESSB8. EDITOBB :—I have been making some experiments for the past three inonthn, widen, I think, -will interest some of your readers. The instrument used consists of a wind vane made of a thin board some four inches long by one twentieth wide, and as thick as a sheet of commercial note paper. In one end are placed four magnets, so arranged that the south poles point down and perpendicular to the vane,; which turns freely on a pivot. The instrument is placed in a box so that the air cannot disturb it. It sounds singular to hear of a wind vane protected from the wind, but, so it is, and I have never, during the entire course of my experiments, found it at fault in indicating the quarter the wind comes from, and that some little time before it comes. The final experiment was made to-day. I placed the instrument at right angles to a meridian traced on the floor, and left it to itself for one hour. When, on returning, I found it lad changed its position, and pointed to the southwest. I timed it, and found that in fifteen minutes the wind came from the southwest (number 1 of the Smithsonian table). There had been nothing of note, in a meteorological point of view, for over one week, so that the magnetic currents could not have influenced the vane. EENE3T TUBNEB, C. E. Philadelphia, Pa. Suggestions about Steam Navigation and Steam Boilers. MBSSBS. EDITOBS :—One of the greatest benefits your valuable journal confers is, that its columns afford a means of ready comniusieation between all classes of inventors—those of the hand as "well as those of the brain ; and thus the floating, useless vimons of the theorist meet, fructify, and utilize the barren fiough vigorous growth of the man of practice alone. The mechanic sets his wheels and gear, and calls for assistance; a -spirit is breathed upon them which animates the mass. Encouraged by such reflections, I venture to send you some of my random ideas for publication. They might be flint to some ones steel. Concisely and briefly, then, in regard to steam navigation: Robert Stevenson said, the problem here was how to diminish the friction of the vessel and the water ; not how to increase the power of engines. Among others, two systems might accomplish this: The discovery of a now instrument, or new application of the old ; or a change of naval construction. First—taking it for granted, I am not quite sure, that the resistance is as the square of the depth, then a lessening of depth, in the water, with same power, would increase speed. We need, therefore, as it were, to raise the vessel. If gas raises a balloon, it should raise a ship, and naturally suggests itself as the means. A ship.contrived by the aid of gas, to draw only one, or a few feet of water, with a powerful engine, would seem, in theory, to solve Stevenson's problem. My objection is, the vast bulk of gas; but my calculations may be wrong. I suggest the use of gas, in tbis manner, as a subject for reflection. I believe ships are now modeled after the fish because nature is supposed to have suggested it. They are made sharp and deep. I suggest, ships do not go through, the water like a fish, but over the water like a duck. The water fowl is nature's model for those things which go over the water, flat, broad, and rounded. The objection of the effect of waves is futile. The center of gravity is at our disposal. Another problem is to lessen the consumption of fuel. Now,a steam boiler consists of water in a metal vessel. When fire is applied, the metal absorbs a vast amount of heat, radiates, deflects, and otherwise destroys the effect of the fuel on the water. This is entirely due to the material of the boiler. What we want, then, is some agent which will hold the steam and water, while it will allow the direct action of the fire on the water—a substance which shall pass rays of heat as fully as glass does the rays of light—a heat-glass. Rock salt does so perfectly, so far as the heat is concerned, but is soluble and combustible. Can not some chemist give us a silicate of sodium which will answer ? GEO. hi. PHELAN. Memphis, Tenn. The Tidal Wave. MBSSBS. EDITOBS :—The SCIENTIFIC AMBEICAN, of November 13th, contains an article on this subject, copied from the London Spectator, and your readers are admonished editorially against overwhelming you with, remarks on the same. It is, therefore, with hesitancy that I venture the following. The drift of the paper quoted, is to show that by the tidal action, tne rotation of the earth on its axis is retarded in consequence of the friction of the water, following the wave in its westerly and opposing direction to the earth's rotation. This is substantially the sum of the proposition. Since the friction of the water is the retarding cause, how would the case stand if there were no water, or if solidified, and itself became friction, leaving a dry earth. Trivial as this assigned cause, friction, appears, to disturb the precision of the earth's rotation, remaining undetected for ages, does it even exist, in an appreciable degree, or if so, is not its tendency to accelerate the rotation ? If we start with, a swell or wave under the moon, the western course of her attraction would keep up the swell from the advancing or western side, and the eastern side would be constantly receding, i. e,., the source of renewal to the swell would be drawn from the advance and its decline eastward, by the retiring attraction of the moon. Hence, the friction of the water, both to and from the swell, would be in favor of acceleration. THOS. W. BAKEWELL. Pitts urgh, Pa. RAT POISON.—Recent experiments have shown that sqills is an excellent poison for rats. The powder should be mixed with some fatty substance, and spread upon slices of bread. The pulp of onions is also good. Rats are very fond of either. —Journal de Okimie.