_Rule in Hydraulics_: (never before published.) To ascertain the velocity of water issuing through an aperture under a given head: Multiply the head in feet by 62, and the square root of the product will show the velocity in feet per second. * * * * * RAILROAD INTELLIGENCE. Old Colony Railroad, from Boston to Plymouth, Mass., has for some time past been in full operation, and is doing a fair business. The whole amount of the stock of the Michigan Central Railroad--$2,000,000--has been taken up, and of course the enterprise will go forward. On the first day of the opening of the subscription books for the stock of the New York and Boston Railroad, the people of Middletown took shares to the amount of $350,000; and they expect to go up to half a million. The Cheshire N. H. Railroad is going ahead rapidly, the grading and bridging on every part of the line being in progress. This road is to be carried over the Connecticut River at or near Bellows' Falls. The stock of the Wilton N. H. Branch Railroad is said to be all taken up. A General Meeting of the proprietors of the St. Lawrence and Atlantic Railway was recently held at Montreal. It appears by the report of the board of directors, that 5,364 shares had been taken up, amounting to about L1,200,000. All parties appear to be confident that this road will be constructed and in operation at an early day. The Little Miami Railroad having been opened to Springfield, is doing a fair business, and adds important facilities to trade in that section. The directors of the New York and Erie Railroad are said to be "going on with it in the right way to accomplish the great object of the undertaking." Contracts are already made for the construction of the road as far as the valley of the Delaware. Proposals for grading 133 miles more are advertised for, which will carry the road to Binghampton, 270 miles from New York. * * * * * It is asserted that of all single marriageable ladies who reached Oregon last season, two-thirds were married before the first of March. * * * * * Alexandria has decided on re-annexation to Virginia, by a vote of 633 to 197. Probably some of her citizens want to be Governors and Representatives. * * * * * The arrival of the new steamship Southerner in Charleston, 57 hours from New York, excited much admiration. She brought 125 passengers; and was pronounced decidedly the handsomest vessel seen in those waters. * * * * * The price of flour at Buffalo, on the 18th inst., was $3.70 per barrel. Corn, 49 cents per bushel. * * * * * Mr. J. B. Gough, who has been for some time seriously indisposed, has nearly recovered his health, and returned north. * * * * *