## 23.11.11

### Happy Birthday Johannes van der Waals

Johannes van der Waals, born November 23, 1837, is famous for his work on the equation of state for gases and liquids which describe the relation between the pressure, volume, and temperature of fluids (gases and liquids). He developed a model in which the liquid and the gas phase of a substance merge into each other in a continuous manner. It shows that the two phases are in fact of the same nature. In deriving his equation of state, van der Waals assumed not only the existence of molecules (which in physics was disputed at the time), but also that they are of finite size, and attract each other. Since he was one of the first to postulate an intermolecular force, however rudimentary, such a force is now sometimes called a van der Waals force.

## 7.11.11

### Happy Birthday Maria Sklodowska Curie

Marie Curie, born  Maria Sklodowska on November 7, 1867. Through several years' unceasing work in the most difficult physical conditions, Maria and her French husband Pierre Curie, processed several tons of pitchblende, progressively concentrating the radioactive substances and eventually isolating the chloride salts (refining RaCl2 on April 20, 1902) and identifying two previously unknown chemical elements. The first, they named "polonium," in honor of Marie's native country, Poland, and the other "radium," for its intense "radioactivity" — a word coined by Marie.  In 1903 she completed her doctoral degree and became the first woman in France to do so.  In the same year, she received her first of two Nobel Prizes.  She is the only person to receive two Nobel Prizes in different fields of science.