Another one here for electricity! I am with Mother Thurber on electricity leaking out of sockets and go around turning off any that have been left switched on with nothing connected! If it can't leak out, why have switches! I do understand how planes stay up in the air and was, thanks to my father, au fait with the mechanics of the motor car, except that now they all think for themselves (mine puts the brakes on at the last minute if I forget to - always useful when you get to my age!). But I marvel particularly at sat nav! How on earth does it know all those millions of routes that people want to travel! You put in a postcode or a street name - it knows where it is! Marvellous!