Lord Kelvin (1824-1907)

Discoveries

Along with a talent for mathematics, Lord Kelvin (William Thomson) had a practical ability for solving problems. This could range from a dripping tap to poor signals from a telegraph cable.

It led him to invent instruments that helped with communication and marine navigation, as well as physics.

Among his main inventions and discoveries were:

• The absolute temperature scale, now known as 'the Kelvin scale'
• The second law of thermodynamics
• Telegraph cables and the galvanometer
• Marine instruments
• A theory about the shape of atoms
• The tetrakaidecahedron.

The Kelvin scale and superconductors

Kelvin realised that it would be useful to be able to define extremely low temperatures precisely.

He noted that molecules stop moving at absolute zero. In 1848, he proposed an absolute temperature scale – now called the 'Kelvin scale' – where absolute zero is 0 kelvin (0 K).

Absolute zero on the Kelvin scale = minus 273.15 degrees on the Celsius scale.

On the Celsius scale, water freezes at 0 degrees. On the Kelvin scale, it freezes at 273.15 kelvin.

Kelvin's definition of the absolute temperature scale is especially important in the field of superconductivity.

Superconductors are materials which are particularly efficient at conducting electricity, but usually only at extremely low temperatures. This phenomenon was only discovered after Kelvin's death.

Second law of thermodynamics

Research into the nature of heat led Kelvin to his formulation of the second law of thermodynamics.

This law states that that heat will not flow from a colder body to a hotter body.

It was first formulated to explain how a steam engine works.

Kelvin's statement of the law says that heat from a high-temperature energy source cannot be entirely converted to 'work'. Some of the heat will be reduced to low-quality energy and 'lost' to the process.

This proved that it is impossible to have a heat engine that is 100% efficient.

Telegraph cables

In 1856 Kelvin became Director of the Atlantic Telegraph Company, which was working to install a telegraph cable across the Atlantic Ocean.

The first Atlantic Cable Expedition in 1857 was a failure.

In 1858, the team succeeded, using an instrument called a mirror galvanometer, invented by Kelvin, to measure electric current flowing through the cable. However only a few weeks later, signals were lost and the quest had to begin again.

After a further failed attempt in 1865, the team eventually succeeded in 1866.

Following the successful installation of the first trans-Atlantic telegraph cable, British expertise in cable-engineering was recognised internationally.

Kelvin's techniques and instruments were used for cables in various parts of the world, including Europe and South America. Many of these cables remained in use until well into the 20th century.

New technologies, like wireless telegraphy, satellite communications and fibre-optics, eventually replaced Kelvin's cables.

Marine instruments

Kelvin was an enthusiastic seaman, used his problem-solving skills to invent several instruments that improved navigation and safety on the sea.

His inventions include:

• Mariner's compass
• Astronomical clock
• Sounding machine

Mariner's compass

From 1870 onwards, Kelvin spent many summers on his yacht.

He invented several instruments to improve navigation and safety. One notable example was a mariner's compass more accurate than any other in existence. This was later universally adopted.

Kelvin's mariner's compass and 'compass card' were installed on the ship HMS Discovery. This is now a museum, berthed in Dundee. See our Places to visit section for more information.

Astronomical clock

An astronomical clock has a number of different dials, showing the relative positions of the sun, stars and planets.

To construct an astronomical clock, you need to determine the motion of various celestial bodies in relation to each other. Even for the Earth alone, this is not straightforward. The Earth does not take exactly 24 hours to make a full rotation around its axis. Also, it 'wobbles' a little on its axis.

Kelvin's talent as a physicist, and interest in navigation, prompted him to create and patent his own version of an astronomical clock in 1869. This was said to be as accurate as any in existence at the time.

Sounding machine

In April 1874, he presented a paper to the Society of Telegraph Engineers on 'Deep Sea Sounding by Pianoforte Wire'. In this paper he described his success in sounding to a depth of 2700 fathoms (just over three miles).

In 1876, Kelvin created a sounding machine to determine the depth of water below a ship. The same year, after the voyage of HMS Challenger, he stated that the old system of sounding by hemp ropes was outmoded.

Later versions of Kelvin's machine became very popular. Motor-driven versions were introduced in the early 20th century.

Most vessels now use echo sounders for depth measurements.

Shape of atoms

In the 1860s, Kelvin became interested in the structure of atoms.

He observed smoke rings, and proposed that atoms were shaped like vortices spiralling around each other. This was similar to the way knots loop and twist.

His hypothesis was accepted enthusiastically for about 20 years. It was later disproved by subsequent scientific research.

Kelvin's work in this field has not been abandoned altogether however. Today related applications include the study of how DNA is coiled and twisted within the nucleus of a cell.

Tetrakaidecahedron

Kelvin modelled a 14-sided figure – a tetrakaidecahedron – to represent a three-dimensional shape with the least surface area.

No one improved on this model until 1993, when Denis Weaire and Robert Phelan described the Weaire-Phelan structure.

The surface area of this structure is 0.3% less than the Kelvin structure, quite a large difference in this context.

When designing the Beijing Water Cube for the 2008 Olympic Games, engineer Tristram Carfrae imagined a structure made of bubbles. Researching the design, he discovered Weaire and Phelan's work, and applied their principles.

Kelvin, then, can be said to have collaborated on the construction of a very impressive and energy-efficient modern building!

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