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Experiments in the rehabilitation of the mentally handicapped

data of visual perception, such as for instance the apparent disappearance of the sugar in water. Sense data however, must remain meaningless unless they are assimilated into a total schema of repeatable actions which are reversible. Irreversible actions are not mental operations, as they may lead to any result whatsoever in an arbitrary manner. It is only when actions are organized into groups of reversible operations that the world for the child becomes stable and predictable despite the changing appearance of reality. The methods used in these studies show the usual idiosyncrasies and shortcomings of the Geneva school at this time. Results are given in the form of individual records, questions are quite variable from child to child and such niceties as reporting the number of children tested in each study are omitted. Sometimes it is hard to flaw the logic of a child, as for instance when asked whether a seed has increased in weight after it has expanded in size through heat, the answer is 'it's heavier because it's bigger, when I was small I weighed less'. However, against the shortcomings of method and the tendency to overtheorize, must be set the now generally recognized completeness of the system, both in its experimental and its theoretical aspects, and the equally well accepted ingenuity and inventiveness of the experimental situations. This makes the book not only entertaining to read, which is a welcome change from most other contemporary psychology books, it also presents the problems to the children in a way that makes sense to them as, after all, clay balls, dissolving sugar, and rising mercury in thermometers are all features of the real everyday world. This contrasts sharply with most of today's far better designed and controlled experiments, where children are usually asked to perform tasks which are quite meaningless to them, and which are not made more acceptable when the experimenter coyly calls them 'a game'. We are still too often faced in developmental psychology with a choice between those studies which, while retaining aspects of real life situations, ask meaningful questions, but in a haphazard and uncontrolled manner, and experiments where a sophisticated methodology is used to deal with trivial and contrived problems.