Page:Popular Science Monthly Volume 12.djvu/447

Rh accenting every second number it is not difficult to run up to six or eight, and still keep the count. In reflecting upon the answers to my interrogatories, I was led to believe that the possession of ten fingers was not the only cause of our counting by fives and tens, but that a certain rhythm in a system of counting by twos enabled us to overcome a resistance to memory.

This point can be elucidated in the following manner: If we desire to keep the count of the letters of the alphabet while we repeat their names, we can arrange them advantageously in a system of squares separated by a clamp of two, as in Fig. 1. Here we A have a system of twos counting up to ten. A system of mental squares, so to speak, is formed, which enables us to hold the numbers apart, and to form a distinct classification. This system is capable of much extension: for instance, we

can readily form another square in which a mental diagram like Fig. 1 is placed again at the four corners of a square, giving us forty; and the system of squares is capable of much further extension before the mind becomes confused and loses its count. In repeating these diagrams in the mind, a certain rhythm will be perceived which is wanting when we use the system of triangles which is represented in Fig. 3, or a system of pentagons or hexagons. Indeed, with the last-named figures great mental confusion speedily arises; the mental resistance to holding a clear image of a square or triangle in the mind is much less than that which arises when we wish to behold mentally a pentagon or a hexagon.

It would not be difficult to prove a close relation between the forms of verse and the instruments by which a mathematician mounts to the expression of thought. The commonest forms of verse are written in four or five feet. In reading such lines the memory retains the rhythm and the words of each line without effort. When, however, we increase the number of feet in the verse, their length becomes cumbrous and the memory flags. No system of squares or triangles can obviate this difficulty. A system of geometrical mnemonics could undoubtedly be based upon the preceding exemplifications.

In the early dawn of human knowledge the arrangement of points in squares and triangles, and the further conception of areas by their subdivision into triangles, undoubtedly arose from the inability of the