away, we obtain an 'after image' of it: must we not suppose that this image existed already while we were looking? The recent discovery of centrifugal fibres of perception inclines us to think that this is the usual course of things and that, beside the afferent process which carries the impression to the centre, there is another process, of contrary direction, which brings back the image to the periphery. It is true that we are here dealing with images photographed upon the object itself, and with memories following immediately upon the perception of which they are but the echo. But, behind these images, which are identical with the object, there are others, stored in memory, which merely resemble it, and others, finally, which are only more or less distantly akin to it. All these go out to meet the perception, and, feeding on its substance, acquire sufficient vigour and life to abide with it in space. The experiments of Münsterberg[1] and of Külpe[2] leave no doubt as to this latter point: any memory-image that is capable of interpreting our actual perception inserts itself so thoroughly into it that we are no longer able to discern what is perception and what is memory. The ingenious experiments of Goldscheider and Müller on the mechanism of reading are most interesting in this regard.[3] Arguing against Grashey, who, in
