The discovery of the law of conservation of energy is an extremely important scientific discovery in the development of physics in the19th century. This law was independently discovered by more than 10 scientists in five countries. Among them, Meyer, Joule and Helmholtz made great contributions to the discovery of the law of conservation of energy. Meyer's work German doctor Meyer first made this important discovery from the study of human metabolism. 1840, Meyer, who was only 26 years old, worked as a doctor on a ship bound for Java. When he drew blood from the sick crew, he found that the patient's venous blood was redder than that in Europe, which caused him to think deeply. He believes that the venous blood of people in tropical areas is red because of high oxygen content, and the excess oxygen is the result of weakening the burning process of food in the body. This made him think of the equivalence of chemical energy and thermal energy in food, and speculated that if the input and expenditure of energy in the human body are balanced, then all these forms of energy must be conserved in quantity. 1842, Meyer published a paper entitled "On forces in inorganic boundaries", which further expressed the idea of energy conservation in physical and chemical processes and put forward the necessity of establishing numerical equivalent relationships between different forces. Joule's Work The British physicist Joule tried his best to prove the immortality of energy through experiments. 1840- 184 1 year, he found that electric energy can be converted into heat energy after many experiments of electrifying conductors to generate heat. 1843, he studied and measured the equivalent relationship between thermal energy and mechanical work, and made a series of experiments, announcing that energy in nature cannot be destroyed. Where mechanical energy is consumed, considerable heat can always be obtained, and heat is only a form of energy. 1847, he did the best experiment to determine the mechanical equivalent of heat. Since then, the experimental method has been continuously improved until 1878, when the average mechanical equivalent of heat is 423.9 kg/kcal. This value is about 0.7% smaller than the recognized value of 427 kg/kcal. Such accurate experimental results provide unquestionable experimental evidence for the establishment of the law of conservation of energy. Helmholtz's work German physicist and physiologist Helmholtz began to study the principle of conservation of energy from physiological problems. On this basis, 1847 published the book Conservation of Force. In this short book, Helmholtz confirmed the role of the conservation law of "force" in nature, gave the quantitative expressions of "force" with different properties, that is, gave the mathematical expressions of different forms of energy, and studied their mutual transformation, so this book became a historical document that had a great influence on the demonstration of the law of conservation of energy. The significance of the discovery of the law of conservation of energy The discovery of the law of conservation of energy is a very instructive example in the history of physics. Because in the process of discovering this law, in addition to the great contributions made by the above three physicists, there are Kano 1824 in France, Mohr 1837 in Germany, Sé gen 1839, a French railway engineer, Hess 1840, a Swiss chemist living in Russia, and Holzman, a German physicist. Grove, an English lawyer, published papers on the conservation of energy independently in 1846, Kohl Ding Yu, a Danish engineer, in 1847 and Elon, a French physicist, in 1854, which contributed to the discovery of the law of conservation of energy. This vividly tells us that the historical breakthrough in physics, personal efforts and talents are of course important factors, but the objective historical conditions (including social, production and scientific conditions) are even more fundamental. Once the conditions are ripe, it is not surprising that a major project is broken by several people or even a dozen people at the same time, which also reflects the historical inevitability. The discovery of the law of conservation of energy is a very important event in the history of physics: ① this law expresses the universal law that the amount of exercise cannot be created and destroyed; This law summarizes all physical phenomena: the phenomena of force, heat, electricity, magnetism and light, which makes it possible to study all these phenomena from the same angle, and regards them as different forms of motion that can be transformed into each other, revealing the unity among these forms of motion, thus achieving the second comprehensive physical science; (2) The discovery of this law also promotes the development of dialectical views on natural phenomena. Dialectics of nature holds that all phenomena in nature should be interrelated.