Place: United Kingdom, United States of America, England, Germany, France
Subject: biography, physics
American-born British physicist who first demonstrated conclusively that heat is not a fluid but a form of motion.
Thompson was born into a farming family at Woburn, Massachusetts, on 26 March 1753. At the age of 19 he became a school teacher as a result of much self instruction and some help from local clergy. He moved to Rumford (now Concord, New Hampshire) and almost immediately married a wealthy widow many years his senior. Thompson's first activities seem to have been political. When the American Revolution broke out he remained loyal to the crown and acted as some sort of secret agent. Obliged to flee to London in 1776 (having separated from his wife the year before), he was rewarded with government work and the appointment as lieutenant colonel of a regiment in New York. After the war, he retired from the army and lived permanently in exile in Europe. Thompson moved to Bavaria and spent the next few years with the civil administration there, becoming war and police minister as well as grand chamberlain to the elector.
In 1781 Thompson was made a fellow of the Royal Society on the basis of a paper on gunpowder and cannon vents. He had studied the relationship between various gunpowders and the apparent force with which the cannon balls were shot forth. This was a topic, part of a basic interest in guns and other weapons, to which he frequently returned, and in 1797 he produced a gunpowder standard.
In 1791 Thompson was made a Count of the Holy Roman Empire in recognition of all his work in Bavaria. He took the title from Rumford in his homeland, and it is by this name that we know him today.
Rumford was greatly concerned with the promotion of science and in 1796 established the Rumford medals in the Royal Society and in the Academy of Arts and Science, Boston. These were the best endowed prizes of the time, and they still exist today.
In 1799 Rumford returned to England and with Joseph Banks founded the Royal Institution, choosing Humphry Davy as lecturer. Its aim was the popularization of science and technology, a tradition that still continues there.
Two years later Rumford resumed his travels. He settled in Paris and married the widow of Antoine Lavoisier, who had produced the caloric theory of heat that Rumford overthrew. However, this was a second unsuccessful match and after separating from his wife, Rumford lived at Auteuil near Paris until his death on 21 August 1814. In his will he endowed the Rumford chair at Harvard, still occupied by a succession of distinguished scientists.
Rumford's early work in Bavaria shows him at his most versatile and innovative. He combined social experiments with his lifelong interests concerning heat in all its aspects. When he employed beggars from the streets to manufacture military uniforms, he was faced with a feeding problem. A study of nutrition led to the recognition of the importance of water and vegetables and Rumford decided that soups would fit the requirements. He devised many recipes and developed cheap food emphasizing the potato. Meanwhile soldiers were being employed in gardening to produce the vegetables, Rumford's interest in gardens and landscape giving Munich its huge Englischer Garten, which he planned and which remains an important feature of the city today. The uniform enterprise led to a study of insulation and to the conclusion that heat was lost mainly through convection; thus clothing should be designed to inhibit this.
No application of heat technology was too humble for Rumford's scrutiny. He devised the domestic range - the ‘fire in a box’ - and special utensils to go with it. In the interests of fuel efficiency, he devised a calorimeter to compare the heats of combustion of various fuels. Smoky fireplaces also drew his attention, and after a study of the various air movements, he produced designs incorporating all the features now considered essential in open fires and chimneys, such as the smoke shelf and damper.
His search for an alternative to alcoholic drinks led to the promotion of coffee and the design of the first percolator.
The work for which Rumford is best remembered took place in 1798. As military commander for the elector of Bavaria, he was concerned with the manufacture of cannon. These were bored from blocks of iron with drills, and it was believed that the cannons became hot because as the drills cut into the cannon, heat was escaping in the form of a fluid called caloric. However, Rumford noticed that heat production increased as the drills became blunter and cut less into the metal. If a very blunt drill was used, no metal was removed yet the heat output appeared to be limitless. Clearly heat could not be a fluid in the metal, but must be related to the work done in turning the drill. Rumford also studied the expansion of liquids of different densities and different specific heats and showed by careful weighings that the expansion was not due to caloric taking up the extra space.
Although the majority of Rumford's scientific work related to heat and its applications, he had an important subsidiary interest in light. He invented the Rumford shadow photometer and established the standard candle, which was the international unit of luminous intensity right up to the 1900s. Transmission of light and shadows cast by coloured sources interested him, and he also looked into concepts of complementary colours. Photosynthesis drew his passing glance and he was probably one of the first to try to relate heat and light in their effects on chemical reaction - the beginnings of the science of photochemistry.
Rumford's contribution to science in demolishing the caloric theory of heat was very important because it paved the way for the realization of the fact that heat is a form of energy and that all forms of energy are interconvertible. However it took several decades to establish the view that caloric does not exist, as the caloric theory readily explained the important conclusions on heat radiation made by Pierre Prévost in 1791 and on the motive power of heat made by Sadi Carnot in 1824.
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