Letter sent from William Gascoigne to William Crabtree
January 25th 1641
William Gascoigne wrote a lengthy letter to his friend William Crabtree of Salford talking about his rudimentary micrometer and a telescopic sight. He also gave advice on how to illuminate the ‘hairs’ suggesting that he was already using the device.
This is the first reference to a micrometer being made and then tested.