Close the eyes and look attentively at what goes on in the field of our vision. Many persons questioned on this point would say that nothing goes on, that they see nothing. No wonder at this, for a certain amount of practise is necessary to be able to observe oneself satisfactorily. But just give the requisite effort of attention, and you will distinguish, little by little, many things. First, in general, a black background. Upon this black background occasionally brilliant points which come and go, rising and descending, slowly and sedately. More often, spots of many colors, sometimes very dull, sometimes, on the contrary, with certain people, so brilliant that reality cannot compare with it. These spots spread and shrink, changing form and color, constantly displacing one another. Sometimes the change is slow and gradual, sometimes again it is a whirlwind of vertiginous rapidity. Whence comes all this phantasmagoria? The physiologists and the psychologists have studied this play of colors. "Ocular spectra," "colored spots," "phosphenes," such are the names that they have given to the phenomenon. They explain it either by the slight modifications which occur ceaselessly in the retinal circulation, or by the pressure that the closed lid exerts upon the eyeball, causing a mechanical excitation of the optic nerve. But the explanation of the phenomenon and the name that is given to it matters little. It occurs universally and it constitutes--I may say at once--the principal material of which we shape our dreams, "such stuff as dreams are made on."