During the past four years the revenue derived from the renta.ge of docks and slips in New York amouted to $1,309,7'10. Of this sum $410,201 were collected during the present year. The first known account of the air-gun is in the Elem ens rl'Ariillerie of David Rivant, the preceptor of Louis XIII. The invention is there ascribed to Mnrtin, of Lisieux, who presented one to Henry IV., (if France. It is calculated that for every million pounds of raw silt produced in France,250 million pounds weight of leaves are consumed, and that five million trees of the average age of thirty years are stripped to furnish them. A geological survey of Georgia is commenced. C. W. Howard has been employed by the Superintendent of the State Railroad to make a survey of the southern slope of Lookout Mountain in search of iron, coal, and petroleum oil. The Minnesota lumbermen are making preparations for logging next winter. Many have already sent up teams and men to prepare the camps, cut outthe roads, and make such other preparations as are necessary before the erews of men arrive inthe fall. Chicago has introduced mounted letter-carriers. The experiment is begun with ten men and ten horses. A new division of the city into districts has also bp.en made. It is exoected that by these arrangements the mail delivery will be better executed than heretofore. Chief Justice Perley, of the Supreme Judicial Court of New Hampshire, has recently ruled that where property is transporter! over a il road line c ompo sed of several distinct roads, the original company, which received it. is liable for the loss or injury, siiould any occur, whether the damage be on its own road or any other. Application will be made to the Parliament ofCanada, at its next session, to incorporate a company for the purpose of making- a tunnel under the Detroit river, to connect the Great Western Railroad with the .Michigan Central, and to secure to other roads terminating either in Hudson or Detroit, the use of the same on fair terms. General Sylvanus Thayer, of South Braintree, Mass., has given $10,000 to Dartmouth College, making a total of $60,000 given by him forthe purpose of founding, in connection with the college, the Thayer School of Civil Engineering. He has also given the college $1.000 as a foundation for two prizes, for proficiency in the higher mathematics. In making a shaft for the new Thames Tunnel, a rotten leather bag was found containing about 300 silver twopenny, fourpenny, an! si"'l:penny pieces of the reigns of Henry III.. of England, and Alexander VII., of Scotland. Just above where these coins were found a broad and weli-paved roa.fi was come upon which was evidently, centuries i.lgo, one of the main routes from Thames street to Tower Keep. The law passer! at the last session of the Massashusetts Legislature, prohibiting theof cars of any description on the railroads of that State . without a brake, went. into effect on October 1) and the penalty for its infraction is $100. On the Concord Hailroad in Nashua the side trades are full of frei ght cat's, many of them 'aden, whi ch the lower roads refuse to run, as they have no breaks attached. M. Brugere introduces anew kind of gunpowder consisting of fifty-four parts ot picrate of ammonia and forty-six parts of nitrate of potassa. He also gives a mixture of twenty-five grms. of picrate of ammonia, sixty seven grms. of nitrate of baryt'1, and eight grms. of sulphur as an excellent substitute for Bengal light, and its suitable for signal aud port lights, and, since hardly any smoke is emitted and no unpleasant smell is given off, for use in theaters. During the last five or six months the engineers employed by the Central Underground Railroad Company have been actively eng-iged in making their examinations and surveys ; and toward the close of the present month, or early the ensuing they will be prepared to pr-esent their reports. No engineering difficulty has been encountered The work willhe commenced as soon as the plans under consideration can be matured in detail, and the contracts for the various kinds of materia) required and workto be performed can be awarded to responsible parties on satisfactory terms.