234 THE DISCOVERY OF THE CHILD A modifying action which increases the power of discrimina- tion is a true and proper educational action. Education of the senses leads to a perfecting of the differential perception of stimuli by means of repeated exercises. There exists, therefore, a sense education which generally is given no consideration in researches made in mental development, but which is a factor which has to be considered. For example, I have often seen used as mental tests cubes varying in size and placed at different distances. From among these the child had to recognize the smallest and the largest,, whilst the chronometer was measuring the time of reaction which elapsed between the-command and the response, and the error was noted. I used to repeat that in. such an experiment the factor of education was forgotten, and by that I meant sense education. Our children have, among the teaching material used.for the education of the senses, a series of ten cubes- graduated in their dimensions. The exercise consists in placing on the ground on a dark-coloured rug all the cubes which are coloured pale pink, and then building up the 6 tower,' placing at the base the largest cube and then the others in succession up to the smallest. The child must choose from the carpet, every time, the largest cube. This game is found to be most amusing even by children of two and'a half years old, who, directly they have built up the tower,, knock it down with little blows, admire the pink shapes .as they lie on the dark background, and begin the construction all over again, for an indefinite number of times. If one of my children between three and four yea,rs of age,, and one of the children from the first class in the elementary school 'between six and seven years of age were exposed to these tests,, mine would undoubtedly show a shorter reaction period and would be much readier to choose the largest cube and the smallest from the heap, and would make, no mistakes. The same may be said about tests in colour sense, tactile: sense, etc.