Distance to the sun discovered by Giovanni Cassini

Born in 1625, Giovanni Cassini was raised and educated in Italy. Invited by Louis XIV, Cassini moved to Paris in 1669 to head the brand-new Paris Observatory. With an improved, high powered telescope that he carefully shipped from Italy, Cassini continued a string of astronomical discoveries that made him one of the world’s most famous scientists. The discoveries include the rotation periods of Mars and Saturn, and the major gaps in the rings of Saturn - still called the Cassini gaps.

The solar distance had a priority in his research program there. Since the value suggested by the measurements in Bologna could have been influenced by variations in atmospheric refraction, it was important use some other method to prove, or disprove the longer Earth-Sun distance scale.

He made the first reasonably correct Earth-Sun distance measurement in 1672 via triangulation. As with triangulation measurement, Cassini first had to establish a base line. Since the orbit of Mars is outside that of Earth, Cassini knew that at some time, Mars would be in a position to provide a proper baseline; accordingly, Cassini decided to measure the Earth-Mars distance to use as his baseline.

He determined the parallax of Mars using observations he made in Paris and those made by Jean Richer in Cayenne, French Guiana. The distance to the sun has always been regarded as the most important and fundamental of all galactic measurements, Cassini’s 1672 measurements, however, was the first to accurately estimate that distance.
Distance to the sun discovered by Giovanni Cassini

Raoult’s Law

Raoult’s Law is named for François-Marie Raoult (10 May 1830 – 1 April 1901) a French chemist who was one of the founders of physical chemistry.  He gave an important law about vapor pressure of the solution, known as Raoult’s law.

He observed experimentally that - in liquid-vapor phase equilibrium of a mixture - the partial pressure of a vapor constituent is proportional to the mole fraction of that constituent in the solution.

Raoult also investigated freezing point depression of solvents when a small amount of solute is introduced. In 1882, Raoult published his results on the effects of nondissociating organic solutes, from which he deduced a general law controlling the lowering of freezing points. Four years later he extended this work to show the effect of solutes on a vapor pressure.

Raoult’s Law is strictly applicable to ideal liquid solutions at all compositions, pressures and temperatures. In an ideal of perfect solution, the components are mutually miscible in all proportions and there are no volume or thermal changes on mixing.

Raoult published the formulations of his laws in the Comptes rendus for 1882 and 1887.
Raoult’s Law