This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
The simplest form of ladder, and suited only to lengths of 12 ft. and under, consists of 2 pieces of good red deal, about 2 in. by 3 in., placed side by side some 14 in. apart, and joined by cross pieces 2 in. by 1 in., at intervals of 8 in., the cross pieces being generally let into notches about | in. deep in the side pieces, and securely nailed or screwed. For ladders of greater length recourse is had to a sound fir pole of the requisite length, which is planed smooth all over, and bored through at 9-in. intervals with a series of 3/4 - or -7/8-in. holes. The pole is then sawn in half down the centre, forming 2 pieces flat on the inside, but rounding on the outside. Spokes cut for the purpose, of ash or oak, are next inserted by one end into all the holes in one side piece, and their free ends are afterwards similarly introduced into the holes of the other side piece. This done, the projecting ends of the " rounds " or spokes are sawn off flush with the outside of the side pieces, a chisel cut is made in each of them (the rounds) in the direction of their length, and these chisel cuts are filled by little wooden wedges driven tight.