To honor their contributions, the names of several scientists have been assigned to the standard units of measurements. In this ScienceStruck article, we present a list of the scientists who have SI units named after them.

### Naming Convention

According to convention, the name of the units of measurement are written in lowercase letters. However, the symbol of a unit derived from the name of a person always has its first letter written in uppercase.

As the wheel of time continues to turn, there are some names which simply cannot be allowed to be lost in its wake. They represent important people who dedicated their lives to the advancement of science. It is owing to their tireless efforts that mankind has been able to reach where it is today.

Throughout history, there have been numerous scientists who have made significant contributions. Though the work of each and every one of them has been instrumental for human progress, there are a few notable from among them who, through their innovative concepts and ideas, completely revolutionized science itself.

To honor them, the International Committee for Weights and Measures has assigned their names to international units of measurements. The International System of Units, known as SI from the French term Système international d’unités, is the most widely accepted standard system pertaining to the units of measurement. It comprises a total of seven base units and 22 derived units, of which two base units and 17 derived units have been named after scientists, thus immortalizing them.

## Units Named After Scientists

### Antoine Henri Becquerel

*1852 – 1908*

**Unit and Symbol**: The becquerel (Bq)

**Quantity Measured**: Radioactivity

**Definition**: Becquerel is an SI derived unit for measuring radioactivity. One Bq measures the activity of a particular quantity of radioactive material wherein one nucleus decays per second.

**Significance**: This unit is named after Antoine Henri Becquerel, who shared the Noble Prize with Pierre and Marie Curie in 1903 for their discovery of the phenomenon of radioactivity.

### Anders Celsius

*1701 – 1744*

**Unit and Symbol**: degree Celsius (°C)

**Quantity** **Measured**: Temperature

**Definition**: The degree Celsius (previously known as centigrade) is the scale and unit of the measurement used for temperature. It refers to a particular temperate on the Celsius scale, and also indicates the difference between two temperatures.

**Significance**: Historically, centigrade was used as the unit for measuring temperature. In the year 1948, it was renamed to degree Celsius in honor of Swedish astronomer Anders Celsius, who had developed a similar temperature scale.

### Sir Isaac Newton

*1643 – 1727*

**Unit** **and** **Symbol**: newton (N)

**Quantity** **Measured**: Force

**Definition**: The newton is the derived SI unit of force. One newton (1 N) is the force required to accelerate one kilogram (1 kg) of mass at the rate of one meter per second squared (1 m/s2).

**Significance**: This unit was adopted in the year 1946 to honor the great English physicist and mathematician Sir Isaac Newton, who was responsible for laying the foundation of most of classical mechanics.

### André-Marie Ampère

*1775 – 1836*

**Unit and Symbol**: ampere (A)

**Quantity** **Measured**: Electric Current

**Definition**: The ampere, known simply as ‘amp’, is the SI unit adopted for the measurement of electric current. One ampere is equivalent to one coulomb (1 C), which is roughly equal to 6.241 × 1018 elementary charge carriers (electrons or protons), moving past a specific point in one second.

**Significance**: French physicist and mathematician André-Marie Ampère was one of the founders of classical electromagnetism, also known as electrodynamics. The unit for measuring electric current―ampere(A)―has been named in his honor.

### William Thomson Lord Kelvin

*1824 – 1907*

**Unit and Symbol**: kelvin (K)

**Quantity** **Measured**: Thermodynamic Temperature

**Definition**: The kelvin is used to measure temperature based on the absolute scale. It is the SI unit of thermodynamic temperature. One kelvin (1 K) is defined as 1/273.16 (3.6609 x 10-3) of the thermodynamic temperature of the triple point of pure water H2O.

**Significance**: British mathematical physicist and engineer Lord Kelvin, the namesake of this unit, wrote a paper in 1848 on the need for a scale wherein the null point would be ‘absolute zero’, and the increment of temperature would be measured in degree Celsius. Lord Kelvin also calculated the value of absolute zero to be -273°C.

### Blaise Pascal

*1623 – 1662*

**Unit** **and** **Symbol**: pascal (Pa)

**Quantity** **Measured**: Pressure

**Definition**: The pascal is defined as one newton per squared meter (1N/m2). It is the SI derived unit for the measurement of pressure, internal pressure, stress, Young’s modulus, and ultimate tensile strength.

**Significance**: Blaise Pascal, a French mathematician, physicist, inventor, writer, and Christian philosopher, made important contributions in the field of fluid mechanics, especially the concepts of pressure and vacuum. The unit of pressure has been named pascal in his honor.

### Charles-Augustin de Coulomb

*1736 – 1806*

**Unit and Symbol**: coulomb (C)

**Quantity** **Measured**: Electric Charge

**Definition**: The coulomb is the SI unit of electric charge. It is defined as the amount of charge transported by a constant current of one ampere in one second. 1 C is equivalent to approximately 6.241 × 1018 protons, and -1 C is equivalent to approximately 6.241 × 1018 electrons.

**Significance**: The coulomb is named after French physicist Charles-Augustin de Coulomb, who made significant contributions to physics, including the Coulomb’s law, the definition of electrostatic force (attraction and repulsion), as well as the study of friction.

### James Watt

*1736 – 1819*

**Unit** **and** **Symbol**: watt (W)

**Quantity** **Measured**: Power

**Definition**: Watt is the SI derived unit of power, which is defined as joule per second. It is typically used to represent the rate of energy conversion/transfer with respect to time.

**Significance**: James Watt was a Scottish mechanical engineer and inventor. He was responsible for the development of the concept of horsepower, and also for improving the efficiency of the Newcomen steam engine, which played a major role in the industrial revolution. The unit of power has been named watt in his honor.

### Alessandro Volta

*1745 – 1827*

**Unit and Symbol**: volt (V)

**Quantity Measured**: Electric Potential

**Definition**: The volt is the SI derived unit used for measuring electric potential, electric potential difference, and electromotive **force.**

**Significance:** Alessandro Volta, the eponym of the unit volt, was an Italian physicist responsible for inventing the first electrochemical battery―the voltaic pile―which led to the birth of the field of electro-chemistry.

### Georg Simon Ohm

*1789 – 1854*

**Unit and Symbol**: ohm (Ω)

**Quantity** **Measured**: Electric Resistance

**Definition**: The ohm is the SI derived unit of electric resistance. The resistance between two points in a conductor is said to be one ohm if a constant potential difference of one volt applied across them, causes a current equal to one ampere to flow between them.

**Significance**: German physicist and mathematician Georg Simon Ohm, while experimenting with the newly developed electrochemical cell invented by Alessandro Volta, discovered that there is a direct proportionality between the applied potential difference and amount of current flow. This relationship is today known as the Ohm’s law, and the unit of measurement of resistance is named ohm to honor him.

### Michael Faraday

*1791 – 1867*

**Unit and Symbol**: farad (F)

**Quantity** **Measured**: Capacitance

**Definition**: The farad is the SI derived unit used to measure electric capacitance, that is, the ability of a body to store an electric charge. The capacitance is said to be one farad, when a capacitor charged with one volt carries a charge equivalent to one coulomb.

**Significance**: Michael Faraday, the namesake of the unit farad, was an English scientist, who is one of the most influential scientists in history. Faraday received very little formal education, and yet made pivotal contributions to the fields of electromagnetism and electro-chemistry. Among his major discoveries are the phenomenon of electrolysis, diamagnetism, and electromagnetic induction.

### Joseph Henry

*1797 – 1878*

**Unit and Symbol**: henry (H)

**Quantity** **Measured**: Inductance

**Definition**: The henry is the SI derived unit of electromagnetic inductance. The inductance in a circuit is said to be one henry if the rate of change of current of one ampere per second (1 A/s) results in an induced electromagnetic force of one volt.

**Significance**: Joseph Henry was an American scientist who is credited with the invention of electromagnets. He is believed to have discovered electromagnetic induction independently at the same time as Michael Faraday, and hence, has been honored by having his name assigned to the unit of measurement of electromagnetic induction.

### Wilhelm Eduard Weber

*1804 – 1891*

**Unit** **and** **Symbol**: weber (Wb)

**Quantity** **Measured**: Magnetic Flux

**Definition**: In the study of physics, the weber is the SI unit for the measurement of magnetic flux. It is defined as the magnetic flux which, linking a circuit of one turn, produces in it an electromagnetic force of one volt if it were reduced to zero at a uniform rate in the time interval of one second.

**Significance**: The unit weber has been named after German physicist Wilhelm Eduard Weber, who, along with Carl Friedrich Gauss, invented the first electromagnetic telegraph.

### Ernst Werner Von Siemens

*1816 – 1892*

**Unit** **and** **Symbol**: siemens (S)

**Quantity** **Measured**: Conductance

**Definition**: Siemens is the SI unit of electric conductance, susceptance, and admittance. It is defined as the reciprocal of resistance, reactance, or impedance.

**Significance**: This unit has been named after German industrialist and inventor Ernst Werner Von Siemens, who was the founder of the electrical and telecommunications company Siemens.

### James Prescott Joule

*1818 – 1889*

**Unit and Symbol**: joule (J)

**Quantity** **Measured**: Energy

**Definition**: In the SI system, the joule is a derived unit for the measurement of energy, work, and heat. It is defined as the amount of work done or energy transferred when a force of one newton is applied through a distance of one meter, or in passing a current of one ampere through a resistance of one ohm for one second.

**Significance**: English scientist and brewer James Prescott Joule studied the relationship of heat to mechanical work. His findings led to the development of the law of conservation of energy, and subsequently to the first law of thermodynamics. The unit of energy is named joule in recognition of his contributions.

### Nikola Tesla

*1856 – 1943*

**Unit and Symbol**: Tesla (T)

**Quantity** **Measured**: Density of Magnetic Flux

**Definition**: Tesla is the SI derived unit which represents magnetic flux density. One tesla is equal to one weber per square meter.

**Significance**: The unit tesla has been named after this Serbian-American inventor, mechanical engineer, electric engineer, physicist, and futurist in recognition of his several important contributions to physics, including the design of modern alternating current (AC) electric supply.

### Louis Harold Gray

*1905 – 1965*

**Unit** **and** **Symbol**: gray (Gy)

**Quantity** **Measured**: Absorption of Radiation Dose

**Definition**: One gray is defined as the absorption of one joule of radiation energy by one kilogram of matter. It is an SI derived unit for the measurement of ionizing radiation dose.

**Significance**: The unit gray has been named in honor of English physicist Louis Harold Gray, who worked extensively on the study of the effects of radiation on biological systems, and who was responsible for inventing the field of radio-biology.

### Rolf Maximilian Sievert

*1896 – 1966*

**Unit** **and Symbol**: sievert (Sv)

**Quantity** **Measured**: Equivalent Dose of Radiation

**Definition**: The sievert is the SI derived unit for measuring the absorption of ionizing radiation. One sievert is defined as the amount of radiation which is nearly equivalent in terms of its biological effectiveness to one gray of gamma radiation.

**Significance**: Prof. Rolf Maximilian Sievert was a Swedish medical physicist. He made a significant contribution to the study of the biological effects of radiation. The unit sievert has been named after him in recognition of his work.

### Heinrich Rudolf Hertz

*1857 – 1894*

**Unit** **and** **Symbol**: hertz (Hz)

**Quantity** **Measured**: Frequency

**Definition**: One hertz can be defined as one cycle per second. It is the SI unit used for the measurement of frequency.

**Significance**: Heinrich Rudolf Hertz was a German physicist who became the first person to conclusively prove the existence of electromagnetic waves, which were predicted by Jame Clark Maxwell’s electromagnetic theory of light. The unit of frequency has been named hertz in his honor.

### John Napier

*1550 – 1617*

**Unit and Symbol:** neper (Np)

**Quantity** **Measured**: Magnitude Based on Natural Logarithm

**Definition**: The neper isn’t an SI unit, however, its use along with other SI units is permitted. It is a dimensionless logarithmic unit representing the ratio of measurements of physical field and power quantities, such as the gain and loss of an electronic signal. It uses the natural logarithmic scale based on Euler’s number (e ≈ 2.71828).

**Significance**: John Napier, who was nicknamed Marvelous Merchiston, was a Scottish physicist, mathematician, and astronomer. He is believed to have invented logarithms, and this unit has been named in his honor.

### Alexander Graham Bell

*1847 – 1922*

**Unit** **and** **Symbol**: bel (B) and decibel (dB)

**Quantity** **Measured**: Magnitude Based on Common Logarithm

**Definition**: Like the neper, the bel and the decibel too aren’t SI units. However, they can be used along with SI units. The bel and decibel are logarithmic units used to express the ratio between two physical quantities, such as power or intensity. The number of decibels is ten times the logarithm to the base 10 of the ratio of the two power quantities. Ten decibels is equal to one bell.

**Significance**: The bel and decibel have been named after the great Scottish scientist Alexander Graham Bell, who invented the telephone.