After the paper on electromagnetic thermal effect and the mechanical value of heat was published, Joule received a cold reception, and many scientists did not agree with Joule's research results. However, Joule was not discouraged, and continued to obtain more accurate thermal work equivalent value through experiments. Until 1878, Joule designed a sophisticated impeller experimental device and conducted more than 400 experiments. Joule measured the thermal mechanical equivalent of water, whale oil and mercury, and almost all the thermal work equivalent values were 423.9 kg m/kcal. This value is only 0.7% less than the currently recognized value of 427 kg m 1 kcal, and this value has remained unchanged for 30 years.