and would have been from 25 to 30 per cent greater if there had been canal boats to do the business The uncertainty of navigation in past years, owing to the liability of low water in the Illinois river, has discouraged boat-building, and the supply of boats is unequal to the demand. These facts point to the most favorable results to follow, upon making the navigation constant throughout the season, along the whole line from the Mississippi to the lake, to say nothing of the great increase which must inevitably follow the completion of the enlargement, affording so much greater capacity and economy. Cheaper transportation attracts a larger amount of freight and increases the revenue even at reduced rates of toll, as is shown by the Erie Canal. The two parts of the work are necessarily dependent upon each other, or rather the canal enlargement and the river improvement make but one work. It will not be worth while to make the one without the other. It is stated that the tolls on the Erie Canal for 1861 were $3,800,000. It cost $40,000,000, and is 352 miles long. This proposed improvement is 316 miles long, of greater capacity than the Erie, and can be completed for $13,346,824. From a fair comparison of the two works, what may be expected of this? It will draw trade from down the Mississippi, from the Rocky Mountains, by way of the Missouri and the Yellowstone. The whole of the western half of the Mississippi system will be naturally tributary to it. While in turn it will pour through its capacious channel the merchandise and manufactures of the East. If, then, the present contracted canal, ninety-six miles long, and without facilities for doing all the business offered in a season of good navigation yields $260,000, may we not firmly expect that when the whole line of 316 miles is opened on the proposed scale, reducing the cost of transportation in proportion, it may yield five time that amount? Or, if the work should cost $13,500,000, the interest on its cost would be $810,000. Taking the tolls to be derived from the enlarged work, shortly after completion, at only four times what they are for the present year, the amount would be $1,040,000, which would pay the interest and loan$230,000 per annum, for repairs and superintendence, etc. Surely this may be considered altogether within bounds, when we look at the growth of the country now going on, and the additional stimulus which such a work would give. The country which will seek this route for its commerce has hardly commenced its agricultural development; hardly one acre in ten is under cultivation, and in large portions not one in a hundred. The want of facilities for transporting produce now represses the growth of this region, by tending to reduce the price of its products below a remunerative point. The East is directly interested in this matter. Any considerable reduction in the cost of transportation here would cheapen the food of every operative in the Eastern manufactories, and tend to draw from Europe the skilled laborers we so much need. Another point is worth mentioning-the effect of such a work in increasing the assessable value of property in the region more directly affected by it. Of course nothing very definite can be arrived at in this direction. Analogy may help us as to some approximation to the amount. One of the projectors of the Erie Canal estimated its effect in this way, in five years, at full $400,000,000; and the differences between the two cases are all in favor of that under consideration. In the vast region communi cating almost immediately with this line, nearly the whole of the land is capable of profitable cultivation, and only waits increased means of transportation to be brought rapidly into use. But is the work national, so that Congress may rightfully execute it? A glance at the map will furnish a sufficient answer. Let the eye follow up the Mississippi, and crossing over to the lakes, dwell a moment upon the line of this work. How little labor and expense will suffice to effect a union between these two great systems of water? As the observer looks and thinks, the greatness of the idea will more and more open upon him. Its military and commercial bearings will develop into vaster proportions, till he will see that nowhere is there a work to compare with it in importance, except perhaps the projected canals across the Isthmuses of Darien and Suez. All of which is most respectfully submitted by your obedient servant, Estimate for a ship and steamboat canal from Lake Michigan to the Illinois river, and the improvement of the Illinois river to the Mississippi river; the canal to be 160 feet wide on the bottom, sides protected with stone walls 10 feet high; the canal and river locks to be 350 feet long and 70 feet wide, with depth of water sufficient to pass steamboats and vessels drawing six feet of water; the canal to be supplied with water from Lake Michigan. Chicago to Lockport, 29 miles: The estimated cost of earth and rock excavation on the summit level from Chicago to Lockport, with walls on both sides 10 feet through the earth, is. Lockport to La Salle, 67 miles: The estimated cost of canal to Lake Joliet, and short canals at sixteen locks, walled on both sides; also six stone dams, 600 feet long, eleven canal and five river locks, each 350 feet long and 70 feet wide-making 138 feet of lockage between Lockport and La Salle-is... La Salle to the Mississippi river, 220 miles: The cost of seven tree and crib dams, 900 feet long, the cribs to be filled with stone and stone abutments; also seven stone locks 350 feet long and 70 feet wide, with entrances protected, and insuring a depth of water on all bars to pass the largest steamboats and vessels drawing six feet, will be... Add for bridges, right of way, engineering, contingencies, etc.. .$7,092,700 4,031,092 1,045,000 578,032 Total. $13,346,824 THE MARINER'S COMPASS-IRON SHIPS. THE Jury at the International Exhibition on Ship Equipments, etc., in speaking of the mariner's compass, observe with satisfaction the progress generally made in the construction of this invaluable instrument. This is progress, they very properly remark, in the right direction; for, with the increasing use of iron in ship-building and fittings an efficient compass is imperative, and thorough efficiency cannot be secured without the greatest care in details and delicacy of manipulation. In 1851 the laws and general principles affecting the compass in iron ships were professionally unknown. They had seriously engaged the attention of a few leading men of science, and so far back as 1839 the present Astronomer Royal of England had made an extended series of experiments by the desire of the Lords Commissioners of the Admiralty in the iron merchant ship "Rainbow." The resulting abstruse investigations did not receive then the attention they merited, though a tentative mode of adjusting the compass published in 1840, by Mr. AIRY, became the basis of a system of compensation since generally adopted in the mercantile marine. The rapid increase of iron built ships subsequent to 1851, and the consequent appreciation of compass disturbances produced numerous plans; some for detecting the deviations without the aid of astronomical or other well known observations, others for correcting the deviations by peculiar arrangements of magnets, and even appliances for isolating the compass from the effects of local attraction appeared; many of these plans resulting from an imperfect knowledge of the laws and mode of action of magnetism were undoubted failures. The melancholy loss of the iron emigrant ship "Taylour," with a great number of her crew and passengers, on the east coast of Ireland, in the early part of 1854, was traced in the main on the official inquiry to the changes of the ship's magnetism, or the imperfect action of the compasses which had been compensated at Liverpool a few days previously to the ship sailing from that port. Public opinion, which was much divided on the subject, eventually invoked the aid of science. A special discussion took place at the British Association at Liverpool in 1854, and ultimately a committee composed of practical and scientific men, interested in the question, was formed at Liverpool for the purpose of collecting information and making the necessary experiments. Three reports of this com mittee, the last dated February, 1861, have been presented to the Board of Trade, this department of government having liberally assisted the inquiry throughout. To this source and to the investigations of the Astronomer Royal and ARCHIBALD SMITH, Esq., F.R.S., with the researches in the same field by other well known names, among whom we may worthily select the president of the Royal Society, General SABINE, we may have every confidence that a secure foundation of the theory and practice of compass management in iron ships is laid, which alone requires the general spread of education to render familiar to the intelligent seamen. The recent improvements in the mariner's compass may be considered under three heads: 1. Independently of the deviation of the compass caused by the local attraction of the ship. 2. As regards arrangements for the correction of the deviation. 3. As regards arrangements of the compass for the purpose of diminishing, but not for the purpose of correcting the deviation of the compass. 1. The principal modern improvements have been the introduction of compound needles, and in the manufacture and fitting liquid compasses, the use of the latter in any excessive motion of a ship or boat being almost indispensable. Sir W. SNOW HARRIS has also introduced a very effective compass, in which the oscillations are much reduced by the application of a thick copper ring in the compass bowl, and allowing the poles of the needles to approach very near to it. By substituting two or more parallel bars for a single bar, which was formerly in universal use, several advantages are obtained, for example, the bars may be placed on their edge, whereby there can be no alteration of their magnetic axes. Greater directive power is obtained with the same weight. Also a combination of two equal parallel bars, of which the ends are 60°, or four, of which the ends are 30° apart, have the moments of inertia about all horizontal axes equal, and oscillations of the card about any axes are performed without any wabbling motion. The following remarkable property also exists: When magnets or soft iron are placed as correctors, unless the needle be very short compared to the distance of the disturbing magnets or iron, a deviation is introduced depending on the length of a needle. This disappears if instead of the single bar needle the compass is composed of two bars, of which the effective ends are 60° apart. The same is the case with the needles, arranged as in the common Admiralty compass, viz.: at 15° and 45° on each side of the diameter. Such compasses are therefore much better adapted for being corrected than single bar needles. 2. Since the attention of the public has been turned to the subject of the deviation of the compass many schemes have been suggested, and many patents taken out for obviating entirely the effect of the iron of the ship on the compass, the projectors overlooking the fundamental law of magnetism that the interposition of a body between the magnet and the needle on which it acts can as little intercept the action of the magnet as the interposition of a body between the earth and another body would intercept the action of the gravitation of the earth, and also overlooking a very obvious consideration, that if any body could intercept the action of the ship's iron, it would also intercept the action of the earth's magnetic force on the needle. The mode of correction by magnets and soft iron is susceptible of so many modifications that a greater number of appliances for this purpose than have been sent to the exhibition might have been anticipated. Two only, the Jury tell us, were exhibited, one the model of a binnacle or steering compass, designed originally for the main deck of the "Warrior," and ships of her class, is exhibited by the Lords Commissioners of the Admiralty. The arrangement thus introduced is remarkable both in itself and also historically. It was many years ago observed that two compasses placed near each other as in the common double-binnacle, would produce a mutual disturbance. A regulation about the time was issued by the Admiralty, forbidding the placing such compasses within such a distance as to allow of the effect being perceptible. It lately occurred to the Superintendent of the Compass Department of the Admiralty (Mr. F. J. EVANS, R. N.) in following up some investigations, that the disturbance thus caused being exactly opposite in direction to that part called the quadrantal, which is found more or less in every iron ship, (but especially large in amount in armour-plated war ships,) might be made use of to correct that error. On the model in question two compasses are arranged side by side, the distance being adjustible, and a scale being given of the amount of quadrantal deviation in a ship which can be corrected at different distances, so that when the quadrantal deviation is found in the usual way by swinging the ship, the compasses can be adjusted to a corresponding distance. This arrangement has also the advantage of permitting the correction of the remaining part of the deviation to be made in both compasses by one set of magnet bars placed between them. In the other arrangement exhibited, magnets are introduced in the bottom of the compass bowl, (which is of the ordinary size,) and the adjustment for different latitudes is made by the application of magnets of different powers. Approval cannot be awarded to this arrangement. The magnets are much too near the compass. The supplying magnets of different power is not only a rude mode of adjustment, but requires much greater knowledge and practical skill than an adjustment by change of distances. 3. The iron ships of the present day have generally iron beams, and sometimes iron decks The effect of this when the binnacle compass is placed on the deck is very serious, and it becomes of great importance to have the steering compass as high above the deck as is consistent with being seen by the steersman, and the Jury conclude that, in any vessel with iron beams, every compass should be at least three feet six inches from the deck. |
