Another skilful personage, called the 'converter,' then makes a tour of the timber-yard, and looks about for all the odd, crooked, crabbed trunks of oak and elm which he can find; well knowing that if the natural curvature of a tree accords somewhat with the required curvature of a ship's timber, the timber will be stronger than if cut from a straight trunk. He has the mould-pieces for a guide, and searches until he has ferreted out all the timbers wanted. Then he sets the sawyers to work, who, with the mould-pieces always at hand, shape the large trunks to the required form. And here it may be noted as a remarkable fact, that although we live in such a steam-engine and machine-working age, very few engines or machines afford aid in sawing ships' timbers. The truth seems to be, that the curvatures are so numerous and varied, that machine-sawing would scarcely be applicable. Yet attempts are from time to time made to construct such machines. Mr Cochran has invented one; and it is said that at the Earl of Rosse's first soiree as president of the Royal Society, a model of this timber-cutting machine was exhibited; that Prince Albert cut a miniature timber with it; and that he thus began an apprenticeship to the national art of ship-building. Leaving the supposed visitor to a ship-yard to trace the timbers through all their stages of progress, we will proceed with that which is more directly the object of the present paper--namely, the relation of _speed_ to _build_. Some sixteen or eighteen years ago, the British Association rightly conceived that its Mechanical Section would be worthily occupied in an inquiry concerning the forms of ships, and the effect of form on the speed and steadiness. The inquiry was intrusted to Mr Scott Russell and Mr (afterwards Sir John) Robison; and admirably has it been carried out. Mr Scott Russell, especially, has sought to establish something like a _science_ of form in ship-building--precisely the thing which would supply a proper basis for the artificers.