From the Chicago Rjpublican. The time has como when ship-bnilding should reccive attention and developmont upon the northwestern lakee. Thora is no other branch of indu-stry, with perhapá the exception of railways, which would so tend to onlargo and develop our agricultural and manufacturing intercsts as tho building of a suíficienoy of iron steamships for the transportation of our surplus products upon our inlaiid waters. The old woodon ship has had its day upon tho ocean. It ought to have its day upon the lakes and rivers of the West and Northwest. Wooden vussels decay much taster, nnd roquire repairs mueh more frequently upon tho lakes than upon the ocean. On account of tho shallowness of our harbors vessels must be built of high draft, and if their length is out of proportion to their depth it is found neecssary in sailing ships to add to the strength and weight of their timbers, and, in steamers, to supplement tho ordinary timbers by a series of arches, which are unsightly and woighty, and which take up a groat deal of cargo spare. An iron ship or steamer, on the other hand, neuds none of these extra uioans for obtaining strength. 8he can be built oi'an unusual length, in proportion to depth. By increasing her beam her powors of fletation can be iircreased in proportion. Thus vessels of this charaoter, with great length, fl.rt doors, light weight of huil, and greator internal space, can curry an immenso" cargo : it is estimatcd froni twenty-five to thirty per cent. more than woodon vessels of the same amount of tonnage. For cinal navigaiion, such as we have on the Weiland and St. Lawrence route, tho superiority of iron over Wooden vessels is immense. They draw so much less water, in proportion to tonnago and capacity, thun wooduii vessels, that they would necessarily earn f rom twenty-fivc to thirty per cent more en the capital sj ent in theil constructiou. Nor is this all. An iron vessel or steamship is'inuch longer lived than a wooden one, and costs lesa for repairs; probably one-third. This is acknowledged to be truo as respects ooeun navigaticn ; but tho adviniagei much more marked upon tho lakes, as the process of oxidation is much slower in freáh water than in salt; while the liability to fonl 011 the botton is reduced to a minimum, as respects the navigation of our in land waters. A wooden vessel on the tho lakes has seen her best days at ten 76818. At fiftoen she is old and will oost so mueh in the way of repairing as in ïuany iiistaucos to rjnder her wholly unprofitable. An iron vessel, on the other hand, will live on tho lakes and do goo l service for from thirty to tiity yeare. Tho Unitefi States government iron steauier Michigan was built over tweuty years ago, and ís to day as sevviceablo as the day on whieh she was XVo venture to say tbai she has cost less for repairs than any Vessel owi.ed by our govornmont. She stitl ses tho boilers and engines with which she was originally supplied. The old English mercantile steanior Great Britain w s built of iron in Bristol, in 1844, and isconsequently nearly twenty-eight yoars old. Yi t wo notico sho is now advertised in the Melbouini! llerald to mako the drct passage froni Australia to England in sixty days. Tho vessel wus it cm time ashore in Dundruin By, on the coist of Ireland, for a wholo winter. No doubt, tiowever, such a vessel would last twice as long upon the lakes as she will ui on the ocean. It will at oncfl be seen, thon, that for tho navigation of the laks iron ships and steamers possess an immense advautage. Thore is no doubt that if we had a sufiiciency of them to supply tho wants of our ïnland commerci, it would reduce the cost of transpovting our produots nearly ono-half. Wo have long hoped to see .orts made in the direction of extonding ;his most important branch of induetry. A few more iron steaniers havo been milt, duHna the ]nst few ycnrs, at Buffalo añil Cleveland. Tliis winter we letona th:it an inercasnd impettu has been give:i to the business. The vessola alroady construotod have proved sorviccii'ilo and have paid well, notwithstanding the high cost of material.