Only geniuses preserve their infantile voracity for 'becauses'-and the naive hope that there are real answers to every question. 'Why is the moon round? Why does the apple fall from the tree? Why are there five planets instead of twenty , and why do they move as they do? Why does milk go sour? Why could the dairymaid not get the pox? Why is the colour of a sailor's blood in the tropics a brighter red than in Hamburg? Why did the frog's legs twitch?' One of the hallmarks of genius is that he has never lost the habit of asking foolish questions like these- each of which led to a momentous discovery.