# About units

Nautical Mile – a unit of length equal to one arc minute of the meridian.

Due to the fact that the Earth has the shape of a spheroid, this length varies from 1842.9 m (at the equator) to 1861.6 m (at the pole). In 1928, by decision of the International Hydrographic Bureau, the length of the nautical mile was taken to be 1852 m.Previously, sailors determined the speed of movement by the time of movement of a wooden block thrown into the water from the bow of a moving vessel to its stern. Since that time, devices for measuring the speed of a ship have been called lags (from English log – “wood chock”).

The lag was a rope with a bar tied at its end. The speed was measured with a lag by counting the number of knots on the rope that were passed overboard over the arm during a given period of time, which was determined using an hourglass. From here comes the term “knot”. 1 knot = 1 nautical mile (1852 m) per hour = 51.44 cm / s.

There are 5 most famous temperature scales:

centigrade, or Celsius (ºC),

Fahrenheit (ºF),

absolute, or Kelvin scale (K),

Reaumur scale (ºR) and

Rankin scale (ºRa)

Fahrenheit

It was proposed in the winter of 1709 by the German scientist Gabriel Fahrenheit. On this scale, the point at which the mercury in the scientist’s thermometer dropped on one very cold winter day (it was in Danzig) was taken as zero.

As another starting point, he chose the temperature of the human body. According to this not too logical system, the freezing point of water at sea level turned out to be + 32º, and the boiling point of water + 212º. The scale is popular in the USA and the UK.

Reaumur scale

In 1731, the French scientist Rene de Reaumur proposed a temperature scale based on the use of alcohol, which has the property of expanding. The freezing point of water was taken as the lower reference point.

The degree of Reaumur arbitrarily determined as one thousandth of the volume that alcohol occupies in the tank and thermometer tube at zero point. Under normal conditions, the boiling point of water on this scale is 80º. The Reaumur scale is now widely discontinued.

Celsius

In 1742, the Swedish astronomer Anders Celsius proposed a scale in which the temperature of a mixture of water and ice was taken as zero, and the boiling point of water was equal to 100º.

A hundredth of the interval between these reference points is taken as a degree. This scale is more rational than the Fahrenheit and Reaumur scales, and is widely used in science.

Kelvin scale

It was proposed in 1848 by the English scientist William Thomson (aka Lord Kelvin) as a more accurate way to measure temperature.

On this scale, the zero point, or absolute zero, represents the lowest temperature possible, that is, a certain theoretical state of matter at which its molecules completely stop moving. this value was obtained by theoretically studying the properties of a gas under zero pressure.

On a centigrade scale, absolute zero, or Kelvin zero, corresponds to -273.18ºС. Therefore, in practice, 0ºС can be equated to 273K. Until 1968, the unit of measurement kelvin (K) was called the degree of Kelvin (ºK).

Formulas for converting Fahrenheit, Reaumur, Kelvin and Rankin scales to Celsius:

Fahrenheit scale translation formulas

Reaumur scale translation formulas

Kelvin scale translation formulas

Celsius scale translation formulas

Rankin scale

It was proposed by the Scottish engineer and physicist William Rankin. Its zero coincides with the zero of thermodynamic temperature, and the size of 1ºRa is 5/9 K. That is, the principle is the same as in the Kelvin scale, only in dimension the Rankin scale does not coincide with the Celsius scale, but with the Fahrenheit scale. This system for measuring the temperature of propagation is not received.