Wenlock first scribbled down her ground-breaking theorem on the magical properties of the number seven at breakfast one day apparently on the back of an envelope, using her usual invisible ink. She then proceeded to send her cousin a letter, using what she later believed to be the very envelope concealing the theorem.Miranda Goshawk, Book of Spells Bridget Wenlock (1202 – 1285) was a famous thirteenth-century English witch and Arithmancer, and the first to establish the magical properties of the