At the present time it has been found that an inclined roof of the olden type is not a necessity over a paper machine, as has been decreed by the tradition passed down from old practices. Within the last year, a number of flat roofs have been placed over paper machines, without any trouble ensuing from condensed water forming on the ceiling and thence dropping upon the stock. It is well known that the use of a flat roof in such places is attended with a great many mechanical conveniences; and the pitched roof hitherto used for these purposes has been submitted to, only because it was presumed to be necessary. The whole tendency of mill design is in the line of fitness of means to ends, in the simplest and most direct manner. When the mills in Lowell were first built, they consisted of isolated buildings, which it was presumed would remain for all time; but when it became necessary to increase the plant, it was found that the engineer had wisely laid out the mills in the same yard in reference to a fixed grade, so that corresponding floors would meet when the buildings were extended so that they reached each other. Wherever a strong and diffused light is necessary for any manufacturing process, or the conditions are such as to require unusual stability of the building, one-story mills lighted by monitors afford accommodations not reached by any other form of construction. In presenting before you some of the salient features of modern mill construction, I have endeavored to show the various steps of progress leading up to the development of the present types of design, as well as some of the methods of construction in present use. These various steps in advance, producing mills better suited for the purposes for which a mill is built, are not generally due to elements originating with the manufacturers, but with the Factory Mutual Underwriters, who, finding it cheaper to prevent a fire than to settle a loss, have in every manner encouraged improvements in construction, equipment, and administration, with the result of diminishing the insurance on textile manufacturing property during the last generation from two and one-half down to one-fourth of one per cent., or reducing the cost of insurance eighty per cent. In designing any work, a careful regard should be given to precedents, remembering that a good designer must also be a good copyist. * * * * * THE PASSIVE STATE OF IRON AND NICKEL.--E. Saint Edme.--The nickel of commerce immediately becomes passive if immersed in ordinary nitric acid. Iron, while being briskly attacked by common nitric acid, is rendered passive by contact with nickel. If steel and nickel are plunged into the acid together, the former metal is not even momentarily attacked. Nickel retains energetically a proportion of combined nitrogen, to which its passivity is due. IMPROVED TORPEDO BOAT.