When we set before our eyes a round globe of any uniform colour, v.g. gold, alabaster, or jet, it is certain that the idea thereby imprinted on our mind is of a flat circle, variously shadowed, with several degrees of light and brightness coming to our eyes. But we having, by use, been accustomed to perceive what kind of appearance convex bodies are wont to make in us;
Geure begien aurrean kolore uniformeko esfera biribil bat-adibidez, urre, alabastro edo atxabitxi koloreko bat-jartzen dugunean, gauza ziurra da esfera hori ikustean inprimatzen zaigun ideia zenbait itzal dituen zirkulu lau batena dela, begietara ñabardura ezberdineko argitasun eta distira heltzen zaigularik.