Fahrenheit hydrometer
The Fahrenheit hydrometer is a device used to measure the density of a liquid. It was invented by Daniel Gabriel Fahrenheit (1686–1736), better known for his work in thermometry. The Nicholson hydrometer, after William Nicholson (1753-1815), is similar in design, but instead of a weighted bulb at the bottom there is a small container ("basket") into which a sample can be placed.