Manufacturers, Agriculturists, Chemists, Engineers, Mechanics, Builders, men of leisure, and professional men, of all classes, need good books in the line of their respective callings. Our post office department permits the transmission of books through the mails at very small cost. A comprehensive catalogue of useful books by different authors, on more than fifty different subjects, has recently been published, for free circulation, at the office of this paper. Subjects classified with names of author. Persons desiring a copy have only to ask for it, and it will be mailed to them. Address, MUNN & CO., 361 BROADWAY, NEW YORK. * * * * * PATENTS. In connection with the SCIENTIFIC AMERICAN, Messrs. Munn & Co. are solicitors of American and Foreign Patents, have had 42 years' experience, and now have the largest establishment in the world. Patents are obtained on the best terms. A special notice is made in the SCIENTIFIC AMERICAN of all inventions patented through this Agency, with the name and residence of the Patentee. By the immense circulation thus given, public attention is directed to the merits of the new patent, and sales or introduction often easily effected. Any person who has made a new discovery or invention can ascertain, free of charge, whether a patent can probably be obtained, by writing to Munn & Co. We also send free our Hand Book about the Patent Laws, Patents, Caveats, Trade Marks, their costs, and how procured. Address MUNN & CO., 361 BROADWAY, NEW YORK. BRANCH OFFICE, 622 AND 624 F ST., WASHINGTON, D. C. * * * * * Transcriber's Note In the original publication the author of 'Coal Tar as Fuel for Steam Boilers' is described as John McCrae in the Contents and John M'Crae in the article header. The second was considered an error and corrected.