MODE OF FASTENING SHEET METAL ON ROOFS, ETC.--Asa Johnson, Brooklyn, N. Y., has petitioned for an extension of the above patent. Day of hearing, May 3, 1871. METHOD OF PRINTING IN COLORS.--Rosalie Croome, Brooklyn, N. Y., has petitioned for an extension of the above patent. Day of hearing, May 3, 1871. MACHINERY FOR COMPRESSING GASEOUS BODIES.--William A. Royce, Newburgh, N. Y., has petitioned for an extension of the above patent. Day of hearing, May 10, 1871. PLOWS.--John S. Hall, Pittsburgh, Pa., has petitioned for an extension of the above patent. Day of hearing, May 17, 1871. CARRIAGE WHEELS.--James D. Sarven, New Haven, Conn., has petitioned for an extension of the above patent. Day of hearing May 24, 1871. * * * * * NEW PATENT LAW OF 1870. INSTRUCTIONS HOW TO OBTAIN LETTERS-PATENT FOR NEW INVENTIONS. * * * * * INFORMATION ABOUT CAVEATS, EXTENSIONS, INTERFERENCES, DESIGNS, TRADE-MARKS, AND FOREIGN PATENTS. * * * * * For Twenty-five years, MUNN & CO. have occupied the leading position of SOLICITORS OF AMERICAN AND EUROPEAN PATENTS. During this long experience they have examined not less than _Fifty Thousand Inventions_, and have prosecuted upwards of THIRTY THOUSAND APPLICATIONS FOR PATENTS. In addition to this they have made, at the Patent Office, _Twenty-Five Thousand_ Special Examinations into the novelty of various Inventions. The important advantage of MUNN & CO.'s American and European Patent Agency is that the practice has been tenfold greater than that of any other agency in existence, with the additional advantages of having the aid of the highest professional skill in every department and a Branch Office at Washington, that watches and supervises cases when necessary, as they pass through Official Examination. MUNN & CO., ASK SPECIAL ATTENTION TO THEIR SYSTEM OF DOING BUSINESS. _CONSULTATION AND OPINIONS FREE._ Inventors who desire to consult with MUNN & CO. are invited to call at their office 37 PARK ROW, or to send a sketch and description of the invention, which will be examined and an opinion given or sent by mail without charge. A SPECIAL EXAMINATION is made into the novelty of an invention by personal examination at the Patent Office of all patented inventions bearing on the particular class. This search is made by examiners of long experience, for which a fee of $5 is charged. A report is given in writing. To avoid all possible misapprehension, MUNN & CO. advise generally, that inventors send models. But the Commissioner may at his discretion dispense with a model--this can be arranged beforehand. MUNN & CO. take special care in preparation of drawings and specifications. If a case should for any cause be rejected it is investigated immediately, and the rejection if an improper one set aside. NO EXTRA CHARGE