Do we not see that the fishes in the sea, when they stretch out their fins and swim about, do always appear larger than their real natural size? And oars too, even though they are very straight, look as if they were broken when they are under water; and things at a great distance display false appearances to our eyes, and in this way do frequently deceive the mind.

For at times inanimate objects have been imagined to be alive, and on the contrary living animals have been considered to be lifeless; sometimes again stationary things appear to be in motion, and things in motion appear to be standing still: even things which are approaching towards us do sometimes appear to be retreating from us, and things which are going away do on the other hand appear to be approaching. At times very short things seem to be exceedingly long, and things which have many angles appear to be circular. There is also an infinite number of other things of which a false impression is given though they are open to the sight, which however no man in his senses would subscribe to as certain.

For quantity in such compounds is measured by fixed limits and rules, and it is not safe either to stop short before one has reached them, nor to advance beyond them. For if too little be applied, it relaxes, and if too much, it strains the natural powers; and each extremity is mischievous, the one from its impotence being capable of producing any effect at all, and the other by reason of its exceeding strength being necessarily hurtful. Again it is very plain with reference to smoothness, and roughness, and thickness, and close compression, or on the other hand leanness and slackness, how very much influence all these differences have in respect of doing good or harm.