The Reynolds number is a mathematical result computed by calculating the ratio of inertial to viscous forces. Put in more understandable English, it measures how fluids move through an area of defined diameter. It is named after English physicist and engineer Osborne Reynolds (1842–1912), who was interested in how water flows through rivers and in waves and tides. However, it can also be used in terms of air flowing through the atmosphere, and thus has applications in meteorology, where Reynolds’s formula is used to calculate air turbulence.