c. The illustration of two philosophical laws, viz., the law of Equilibrium or Balance, and the law of Transmitted Motion or Propagation of Force.
4. Progress is shown in this gift as follows:—
a. In the difficulty of dictation and manipulation arising from the different character of the faces of the bricks, and the many positions which each brick can assume.
b. In the necessity of perfect balance.
c. In a clearer illustration of dimension. In the third gift the parts were equal in height, breadth, and thickness; in the fourth they are unequal, and therefore each dimension is emphasized.
As to progression, the increase of difficulty suits the increase in the child's power of comprehension and receptivity. He is being developed thus far, not by rapid changes in material or greater exercise in number, but by practice with differing forms, each one bringing with it new knowledge and experience. The organs of perception are being constantly made to grow by exercise with intention. We are forming the scientific eye which can detect differences ever after at a glance.
5. The geometrical forms illustrated in this gift are:—
| Solids. | { Rectangular Parallelopipeds. |
| { Square Prisms. | |
| Planes. | { Oblongs. |
| { Squares. | |
6. The fourth gift presents contrasts of dimension and, as to the area of its faces, contrasts of size and their mediation.