The rungs of such a “duck” ladder are merely nailed to the outside if the ladder is required for temporary purposes only; but as we are of course aiming at the construction of a thing made to last, we shall go to the trouble of “notching-in” each rung (see Fig. 10), so that the sides shall take the weight directly, and the nails only have to keep the rungs firmly in position.  The objection to notching-in is that it reduces the strength of the ladder, which is of course only that of the wood between the bottom of the notches and the plain side.  Therefore it is necessary to have sides somewhat deeper than would be required for a centrally-runged ladder; which is pierced where the wood is subjected to little tension or compression.

[Illustration:  Fig. 10—­House ladder and details of letting in a rung]

Materials.—­The length of the ladder will decide what the stoutness of the sides should be.  For a ladder about 12 feet long, such as we propose to describe, larch battens 3 by 1-1/8 inches (actual) in section and free from knots, especially at the edges, will be sufficiently strong to carry all reasonable weights without danger of collapse.  But be sure to get the best wood obtainable.  The rungs may be of 2 by 1 inch stuff, though 2 by 3/4 inch will suffice for the upper half-dozen, which have less wear, and are shorter than those below.

The rungs are 10 inches apart (Fig. 10), centre to centre.  The distance may be increased to a foot, Or even more if weight-saving is an object.

CONSTRUCTION.

Preparing the Sides.—­These are cut to exactly the same length, which we will assume to be 11 feet 6 inches, planed quite smooth and rounded off slightly at the corners to make handling comfortable.  Before marking them for the rungs it is important that they shall be so arranged that both incline equally towards a centre line.

Stretch a string tightly three inches above the ground, and lay the sides of the ladder on edge to right and left of it, their ends level.  Adjust the bottom ends 8-1/2, the top ends 6-1/2 inches from the string, measuring from the outside.  Tack on cross pieces to prevent shifting, and then, starting from the bottom, make a mark every 10 inches on the outside corners, to show the position of the tops of the rungs.  A piece of the wood to be used for making the rungs of is laid up to the pairs of marks in turn, and lines are drawn on both sides of it.

Cutting the Notches.—­The work of marking the ends of the notches will be quickened, and rendered more accurate, if a template (Fig. 10) is cut out of tin.  The side AC is 3/8 to 1/2 inch deep.  Apply the template to both faces of the side in turn, with its corner A at the line below the rung, and de flush with the upper corner.  When all the notches have been marked cut down the AC line of each with a tenon saw, and chisel along BC till the wedge-shaped chip is removed.  Finish off every notch as neatly as possible, so that the rungs may make close contact and keep water out.