A well-to-do father provided his son with brilliant home education including mathematics, chemistry and physics. Joule’s teacher of physics was John Dalton, a famous scientist. Under his influence, at the age of 19, the son of the brewer began conducting physical experiments. At the age of 23, he proved that the heat emanated by the conductor when the electric current was passing through it is proportionate to the square of the strength of current and the conductor’s resistance. The same law was discovered independently by Russian physicist Lenz, therefore, in Russian textbooks this law is referred to as the Joule-Lenz law. A couple of years later Joule, who was still young, discovered the second law now bearing his name: it states that the internal energy of perfect gas depends only on its temperature and does not depend on its volume.
The list of discoveries made by Joule could have taken 10 more lines, yet his first achievement all encyclopedias mention is the experimental proof of the law of energy conservation. For those who do not remember the first principle of thermodynamics, as this law is referred to alternatively when applied to thermodynamic processes, we cite its most simple wording: it is impossible to create perpetual motion that works without taking energy from any source.
However, the man who formulated the main law of physics was a product of his era: for example, he believed that electric engines would never replace horses as he calculated that the cost of zinc used in the battery well exceeded the cost of oats eaten by horses while it would perform the same amount of work.