Gabriel Daniel Fahrenheit is a German physicist born in Danzig in 1686. He is the inventor of the mercury thermometer. The zero point of his temperature scale was originally based on the coldest day in Danzig in the winter of 1709-- a thermodynamically legitimate zero point but one difficult to reproduce in the laboratory. James Prescott Joule was an English physicist who lived from 1818 to 1889. He is famous for his contribution to the understanding of the nature of heat. His most important scientific work was done when he was only 25 years of age. Joule's achievements were widely recognized during his lifetime, and he was honored in many ways. It is interesting to note that Joule was educated privately and that he was not associated with any university. Nicolaus Otto (1832-1891), German engineer credited with constructing the first successful internal-combustion engine. Otto received an American patent in 1877. The demonstration engine which Otto used when applying for the patent is now in the Smithsonian Institution. Nicolas-Leonard Sadi Carnot (1796-1832) graduated from the Ecole Polytechnique (a French military school) in 1812 and was commissioned in the Engineers Corps. He published a profound scientific work in 1824, in which he laid the foundation for the second law of thermodynamics. The cycle which bears his name forms an important concept in his discussion. It is interesting to note that Carnot's work, which contains the essentials of the second law , was published before the first law was enunciated. William John Macquorn Rankine (1820-1872) was a Scottish engineer and physicist. In 1855 he became professor of civil engineering in Glasgow. Rankine was interested in the fundamental as well as in the applied aspects of thermodynamics. His name is also connected with the basic steam-power cycle. Amadeo Avogadro was an Italian physicist who lived from 1776 to 1856. In 1820 he became professor of physics in Turin. John Dalton (1766-1844) was an English chemist and physicist of great renown. He was for some time a professor at the New College in Manchester but resigned this position when the college was moved. After that Dalton continued to instruct as a private teacher. His most famous pupil was J. P. Joule. Johannes Diderick van der Waals (1837-1923), a Dutch physicist and professor of physics at the University of Amsterdam from 1877 to 1907. Rudolf Diesel (1858-1913) was a German mechanical engineer and the designer of the type of engine which bears his name. Diesel died in a some-what mysterious accident when he fell overboard on a trip across the channel from Antwerp to Harwich..