Seeing that it cannot with any show of reason be affirmed that the boiler covering materials in present use possess the requirements necessary to recommend them; the question arises as to what is the best means of achieving the object required. This is an inquiry which it is the office of time alone to answer. As the problem is obviously one of primary importance, and well worthy of the attention of inventors, it is hazarding nothing to predict its satisfactory solution at no distant date.

The plain truth is, boilers have of late become gigantic foes to human life. Explosions have increased, are increasing, and should be diminished; and they are, in many instances, caused by boilers being strained and weakened by sudden contraction from having their surfaces exposed when the fire has been withdrawn from them. Boilers are also materially injured by the excessive furnace heat which it is necessary to maintain to compensate for the large amount of caloric which is dissipated from their surfaces, not only by radiation but from absorption by the surrounding atmosphere.

As the views here laid down are drawn exclusively from the region of fact and experiment, it is to be hoped that an enlightened sense of self-interest may prompt those whom the subject may concern, to give it that special attention which its importance demands.

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Attachment of Saws to Swing-Frames.

To insure the efficiency of mill-saws, it is highly important to have them firmly secured in the frames by which they are reciprocated. Swing-frames for carrying saws are ordinarily of wrought iron or steel, and made up of several pieces mortised and tenoned together in the form of a rectangular frame or parallelogram, of which the longest sides are termed verticals and the shortest crossheads or crossrails. In the case of deal frames, the swing frame differs somewhat from that of a timber frame, in having two extra verticals, which separate it into two equal divisions. These are necessary in order that two deals may be operated upon simultaneously, each division being devoted to a separate deal, and likewise to enable the connecting-rod which works the frame to pass up the center and oscillate on a pin near the top, thereby avoiding the deep excavations and costly foundations required where the rod is engaged with the pin at the bottom. The rack that advances the deals to the saws passes through a "bow" in the connecting-rod and the middle of the frame, the deals are placed on either side of it, on rollers purposely provided. In sawing hard deals, the saws require to be sharpened about every tenth run or journey, and every twentieth for soft. Fifty runs, or one hundred deals, are reckoned an average day's work; this is inclusive of the time required for changing the saws, returning the rack for another run, and other exigencies. For attachment to swing-frames the saws have buckles riveted to them; these are by various modes connected to the crossheads. Each top buckle is passed through the crosshead and is pierced with a mortise for the reception of a thin steel wedge or key, by whose agency the blade is strained and tightened. The edge of the crosshead upon which the keys bed is steeled to lessen the wear invariably ensuing from frequently driving up the keys. The distances between the blades are adjusted by interposing strips of wood, or packing pieces, as they are termed, of equal thickness with the required boards or leaves; the whole is then pressed together and held in position by packing screws. The saws themselves are subsequently tightened by forcing home the keys until a certain amount of tension has been attained, this is ascertained only by the peculiar sound which emanates from the blade on being drawn considerably tight and tense. Great experience is required to accustom the ear to the correct intonation, as in general the tensile strain on the saws