The word "barometer" literally means "weight-measurer" or "pressure-measurer". Barometers precisely measure atmospheric pressure. The oldest instrument designed to measure the pressure of the air is probably the so-called "weather glass". Depending on the pressure of the atmosphere, the level of liquid would either rise or fall inside a specially crafted carafe with a long "beak". At the beginning of the 17th century, G. de Donckere built such "weather glasses" in the Netherlands, where they were known as "thunder flasks". Mariners relied on them to indicate impending changes in the weather. Modern barometers can reliably indicate weather trends 24 to 48 hours in advance.