The heaviest cog-wheels in the world—always excepting Mr. I Sherwood's screw steamships—are to be found in iron rolling mills. Nothing at all resembling this gear is to be discovered in floor or cotton mills, or in any other situation on land where steam power is employed. Spur-wheels 18 ft. to 25 ft. in diameter, 24 in. wide on the face, and 8 in. or 9 in. pitch, are not uncommon; while pitches of 6 in. and widths of 18 in, and 20 in. may be met with in almost any little rolling mill we can enter. The quantity of gearing employed in driving an ordinary rail or forge train is even more remarkable than its dimensions. First, we have a tremendous spur-wheel on the engine shaft, working into a pinion on the flywheel shaft, which gears again into a spur-wheel, on the shaft of which is a square end to take the coupling-box and breaking-spindle to the rolls. We have, in this arrangement, three spur-wheels and six bearings, all of the largest and heaviest class; and this, be it observed, is rather a simple mill than otherwise. When a hammer, a shears, and a second train have to be driven, we generally find as much gearing as would fill a good-sized modern dwelling-house, running at a high velocity, for the most part badly put to work, and, therefore, noisy and liable to accident. It is not too much to say, in fine, that at least one-half of the whole power developed is expended in keeping this gearing in motion; while its first cost represents one-half the capital invested in the plant of any iron mill. It is worth while, under such circumstances, to consider whether gearing may or may not be dispensed with; and whether we can or cannot improve upon arrangements admittedly objectionable if tested by comparison with other mills. In dealing with the subject, we must first ascertain why gearing is used at all. This point is soon settled. The velocity at which ordinary trains run varies between 40 revolutions per minute for sheet mills and 100 revolutions per minute for bar or rail mills. Higher and lower velocities are met with, no doubt, but the two which we have named are those most usually adopted, and all that we shall say on this subject just now, will be sufficiently illustrated by cases afforded by those two speeds. Now the work to be done in rolling iron is excessively variable, and it is, therefore, necessary to employ great fly-wheel power, in order to store up force at one time, sufficient to carry the bar, rail, or sheet, through the rolls at another. Without going into mathematics, we may state here that the force afforded by any fly wheel for overcoming the resistance offered to the rolls of a train, varies as the square of the number of revolutions, the weights being the same. Thus, a fly wheel running at 80 revolutions per minute, would be practically four times as efficient as one similar in all respects, and running at 40 revolutions. Therefore, it has come to be looked on as an axiom by rolling mill engineers, that the fly wheel cannot be run too fast. As a consequence, in old works, we always find it put on a second-motion shaft, never on the engine shaft. In the endeavor to obtain high flywheel speed, we find the first cause for the introduction of gearing in rolling mills. * The second reason lies in tlie fact that until a few years back, slow moving engines of great size were alone employed to drive sheet and rail'trains. These engines had a long stroke, and ran at but eighteen or twenty revolutions per minute. This being too slow for any but blooming rolls, gearing became a necessity. The enormous dimension usually imparted to rolling mill gearing, is explained by the fact that it is exposed to many shocks and jerks which are peculiar to the work which it performs, and that for the most part it is roughly and cheaply made, and carelessly put together. We have, we believe, given in the foregoing paragraphs, every valid reason which can be alleged in favor of the use of clumsy, heavy, costly gearing in rolling mills. It remai-ns to be seen whether these reasons are or are not incontrovertible. Taking the last phase of the question first, we may state that during the last few years better materials, better proportions, and superior workmanship have been introduced by many makers, such as Claridge, North & Co., and others, with a view to keep down the weight of mill gearing, and with much success, especially in Staffordshire; and it is, beyond question that still more may be done in this direction. But it is quite in another way that we must look for radical improvement. We must begin at the fountain head, and instead of heavy, lumbering, slow working engines, resort to the use of machines making a fair number of revolutions without an excessive piston speed. A good deal has already been done in this direction, we are happy to say. At Woolwich arsenal the splendid bar mill is driven direct at some 60 revolutions per minute by a horizontal engine. In this case power is stored up in one of the finest fly wheels in England, weighing 50 tuns. The sheet train of the Warrington Wire Iron Company is driven direct by an engine fitted with a 60-tun fly wheel. These great weights are rendered necessary by the comparatively slow speed of the trains. When velocities of 100 revolutions are attained a 20-tun wheel will answer every purpose. As an illustration we may cite the Pendleton works, near Manchester, where a 16-in. rail mill is driven direct at 100 revolutions per minute, by a horizontal engine with a 26-in. cylinder and 4 ft. 6 in. stroke. This engine has been running constantly for the last fifteen years, with few or no repairs. The advantage of this system cannot be over-estimated. The cost of a great mass of heavy gearing is saved; the price of the engine is not nearly that of a larger and slower running machine ; the chances of breakdowns are reduced to a minimum; and the expense of repairs, wear and tear, and lubrication, is-obviously very greatly diminished. When, as in sheet mills, the rolls run too slowly to permit the engine to be coupled direct to them with advantage, the best plan will still be to use a small engine, running at some 70 or 80 revolutions per minute, and carrying on its shaft a spur-pinion gearing into a spur-wheel on a second-motion shaft driving the rolls direct; we thus retain a high velocity in the fly-wheel and a cheap engine, although some of the disadvantages connected with the use of gearing, unavoidably remain. The gearing at present usually employed in reversing mills consists of no fewer than five huge spur-wheels and pinions, beside the clutch-boxes. The entire arrangement is simply a barbarous relic of the past. Reversing mills should be driven by small, high-speed coupled engines, withoufly wheels, and fitted with a link motion. The first cost is not greater than that of the ribrmal arrangement, while the waste of power and the chances of derangement are greatly reduced. Those who wish to realize what can be done in this direction, should see for themselves engines and mills designed by Mr. Ramsbot-torn for Crewe, and others manufactured by Messrs. Tennant, Walker & Co., of Leeds, for America. The above is from the Engineer. There are many mills in this country to which these criticisms apply. But the greater number of our rail mills have engines coupled directly to the trains—vertical engines, too, which take up the least room. And, for work no heavier than rails, our three high mill is a vast improvement on the reversing mill. Indeed, with proper lifting gear, it is probably better for the heaviest work, such as 15 in. beams. In some of the new English rail mills, two or even four trains are connected to a single engine by no end of cog-wheels. We can copy the English practice with advantage in many cases; but in the matter of rail mills, our neighbors should study our practice, for instance at Reading, where they would see three 23-inch 3-high trains, driven each by its own direct vertical engine, at 60 to 80 revolutions; at Harrisburp1, where a 40 in. by 60 in. direct vertical engine drives a 24-in. 3-high steel train, four rolls long, at 60 revolutions; and at Johnstown, where a similar engine, with a 60-tun fly wheel, drives, direct, a 21 in. puddle train five rolls long, and two squeezers. — Van JVostramfs Engineering Magazine. Relative Merits of Wire Ropes and Chains for Hoisting Ores. Mr. Warrington Smith, in his lectures at the Eoyal School of Mines, in London, thus discusses the relative merits of wire ropes, hempen ropes, and chains for hoisting ores : " As regards size and strength, these vary considerably. When only manual labor is employed, and the weight lifted is, perhaps, not more than 1 cwt., a very light chain or rope would do, but when we come to steam power, and have to lift several tuns at once from great depths, as in the north of England collieries and iron mines, the rope must be of extraordinary strength. The ordinary rope of three strands was used for many centuries, until a practice grew up in the deeper mines of employing flat ropes, which were found to go down and up in an even plane, and more steadily than round ropes, which are constantly twisting about. In 1830, in the Hartz mines, the question of the amount of money swallowed up in the wear and tear of ropes came under discussion, and it was proposed to make the rope of iron wire, which was then largely tried not only there, but in other parts of Europe, although at first there was great prejudice felt by the men against it. They like a good thick rope, which was very natural, for in travelling up and down these great depths men did not fancy trusting their lives to a little rope not thicker than their thumbs. They were, however, found to be consistent with great economy. They were made of three strands, with a very slight amount of twist, each strand containing a greater or less number of wires. After a while the ropes were made round, with a hempen core, but as in use they were found to have a great deal of torsion, beside not wearing well, in consequence of their not being well looked after and cared for in passing through the shafts, and thus the wire became apt to break, so that you might often see a rope with pieces of wire projecting from it. Whenever this was seen it became high time either to condemn the rope altogether as useless, or to have the shaft examined at the places where it came into contact with the rope, to prevent further damage. In collieries the ropes are carefully protected from coming into contact with the side, and they last very well. The advantages of wire are very considerable. The prime cost is not much less, but a given weight of wire-rope will support a much greater burden than a hempen rope will/so that when an engine is taxed to the utmost, and can only raise a small amount of mineral, the adoption of wire rope would enable it to raise more. Another substance used for ropes, with a considerable advantage, is the fiber of the American aloe, used largely in France and Belgium. At the Grand Hornu some observations were made in order to test its usefulness. At one of the shafts there (No. 8), 355 meters deep, where four tubs are raised at a time, the rope is flat, made of aloe, and consists of six ropes, of three strands each, bound together; this did excellent work, and compared favorably in durability and efficiency with ropes made of other materials. It is usual to make the ropes taper, because the lower end has the weight to sustain all through the operation, while the upper part passes round a drum, and so has a less proportion of weight to sustain. Chains are frequently employed, and in metalliferous mines perhaps more than anything else. They are mostly single-linked chains, and differ considerably in weight per fathom. In collieries they are largely employed, even to a depth of 450 yards, and the men are lowered to and from their work by this means. It is, however, a dangerous thing to.trust men's lives to a aingle-linked chain, as a flaw in the iron or a bad joint might produce the most fatal consequences, and of late the practice has been very much discontinued, except, perhaps, in the Cornish mines, although it is not uncommon for tolerably new chains to break in a sudden and unexpected manner. Chains are very useful in metalliferous mines, because they may be easily twisted and turned round sharp Corners, which is not the case with ropes, which, when large and strong, have a great amount of rigidity. If chains are used they ought to be made of the best charcoal iron, no matter what the cost may be, and care should be taken that the maker is a careful man, and understands the nature of his work. A good chain-maker is a person who deserves high pay, because a great amount of responsibility rests on him. Chains, also, ought to be frequently overhauled, brought up out of the pit, well washed, and every link carefully examined, which, if it were done more frequently and more systematically, would keep down the number of accidentsconsiderably. In some districts, to obviate the danger of sudden fractures, a compound instead of a single-link chain is ured, and occasionally a stub of wood is driven through every alternate link to prevent kinks when it passes round the drum. Although the wire rope has a great superiority over the ordinary hempen rope or chains, it requires to be lised with great caution, for if it be turned over a barrel of too small a diameter, it will not last long; and may ehap rery suddenly. This makes it, as a rule, inapplicable to v.indlass works in metalliferous mining, or, indeed, in the coal fields, where the operations are preliminary, and only conducted for the purpose of searching. A wire rope never ought to be carried over a windlass or pulley of less than 3 ft. in diameter, and when the rope is of great strength, not less than 6 it. This, therefore, puts the employment of wire-rope with a windlass quite out of the'question, as no ordinary windlass has the requisite diameter. Where, however, special arrangements are made, and a drum of 3 ft. diameter is adopted, it may be used, and I could mention examples in which the wire rope has done good service under those circumstances. For instance, in Austria, at a certain pit, 47 fms. deep, where two drums were used, the smaller of which was 32 in., experiments were made, and without going into particulars as to time of filling, etc., the amount raised by one man in seven hours was 1,269,634 foot-lbs., or 3,141 per minute, by the second 1,175,411 foot-lbs., or 2,902 per minute, which, reduced to the usual standard, will give results considerably in excess of those laid down by most authors, and, as you will remember, of Professor Weisbach, who gives 2,448, ana Mr. Walker, the late President of the Institute of Civil Engineers, who gives 2,640. Exceptionable kinds of windlasses are sometimes devised to meet peculiar circumstances ; as, for instance, in the extraction of the brown coal obtained in the south of France they use windlasses at which four men can work at once. Perhaps, however, there is no nation which understands the use of the windlass better than Spain, as in the mountainous parts of their mining districts they have no water power available. Indeed, water has frequently to be carried by mules up to the mines for the use of the men. The amount of work performed by the windlass there is very large, the apparatus being contrived on a large scale, so as to employ four men in turning it. There is only one other exceptional kind of windlass that I need mention, and that is where in some foreign countries, in slate quarries, the drum is turned into a sort of treadwheel, with steps put on the side upon which men walk. The capstan is not much used, except in particular districts. Considering the great extent to which this apparatus is used, and the great attention paid to many of its details, it is rather wonderful that no better means have been devised for the safety of the men who are lowered and drawn up in these workings. Their lives hang upon a mere thread, and, to say nothing of the rope breaking, any accident to men at the windlass would let the kibble, tub, or bucket go with a run to the bottom. In the north of England, however, they do use a clevis or spring hook, so as to prevent the possibility of accidents of this Mnd. A Valuable Scientific Museum Destroyed. The St. Louis Academy of Science has recently suffered the loss by fire of its valuable collection of books, pamphlets, maps, etc. The museum contained six hundred specimens of marine shells, donated by the Smithsonian Institute, and was unusually rich in crania, skeletons of birds, and reptiles, together with Dr. Pope's mounted skeletons of mammals, purchased in Europe and transported at great expense; also about 1,200 specimens of minerals, embracing a full suit of Missouri minerals and ores. There were also an extensive collection of the bones and teeth of extinct animals, and fossil turtles collected from the Mauvais Terre, Dakota, by Prof. Hayden ; also the collection of rocks, illustrating various geological periods, amounting to four or five hundred specimens, including those collected by Dr. Wizlizenus during Colonel Doniphan's expedition to New Mexico. Beside the above, there were any quantity of Indian relics and curiosities, including a birch bark canoe ; also the specimens of porcelain, collected from a porcelain tower blown up by the China rebels, and presented to the Academy by Lieut. Clarke, United States Navy. All were destroyed, a loss which is irreparable. FREE TRADE.—It is believed by many of our most careful thinkers that the present unsatisfactory financial condition of the country grows chiefly out of our excessive foreign importations. At the present rate the imports for the year will exceed the exports by more than $100,000,000, which difference must be made up in coin or its equivalent. This seems to be a plain matter of fact, and one that all can understand. Our present tariff, although rating very high, brings us in debt to foreign nations a hundred millions per annum. Now what would be the effect if we should adopt the principle of free trade ? It seems to us that our country would soon be filled with foreign goods at prices far below the cost of their production here. Result—prostrate manufacture, idle hands, dull market towns, poor farmers, and a general stagnation. In other words, free trade means destruction to home industry.