What is rain gauge? Who invented it? What is the idea behind it?

A rain gauge is an instrument used by meteorologists and hydrologists to gather and measure the amount of liquid precipitation over an area in a predefined period of time. In 1662 the first tipping bucket rain gauge was invented in Britain by Christopher Wren and Robert Hooke.  The idea behind this instrument is to measure the precipitating rain in a given amount of time per unit area