74. The principal questions relative to the action of forces on single beams, and on systems of framing, have now been considered; and it only remains to make a few remarks on the best method of applying those principles so as to form a perfect design.

In the first place, the artist must remember "that the strength of a piece of framing, whatever may be the design, can never exceed that of its weakest parts; and that partial strength produces general weakness." *

Therefore, let the fixed conditions, or those parts which cannot be altered, be well considered; and as far as it can be done, let them be drawn correctly to a scale; showing the curves of equilibrium, the points where the forces act, and every other particular condition. Also, it must be considered whether the forces are to act constantly on the same parts, or to be subject to changes; and the nature and extent of these changes should be exhibited.

2ndly. The nature of the sustaining points should be carefully examined, whether they be capable of resisting a force acting obliquely against them or not; and the framing must be disposed accordingly.

Then a design may be sketched in, of such a nature as shall appear best adapted to attain the objects in view; the strength of the parts being fixed by the rules in the next section.

Nothing will assist the artist more in forming a good design than just conceptions of the objects to be attained; and nothing will render those objects more familiar to his mind than drawing them.

Seppings' ' Philosophical Transactions.'