<P> Boyle is also credited for his landmark publication The Sceptical Chymist in 1661, which is seen as a cornerstone book in the field of chemistry . In the work, Boyle presents his hypothesis that every phenomenon was the result of collisions of particles in motion . Boyle appealed to chemists to experiment and asserted that experiments denied the limiting of chemical elements to only the classic four: earth, fire, air, and water . He also pleaded that chemistry should cease to be subservient to medicine or to alchemy, and rise to the status of a science . Importantly, he advocated a rigorous approach to scientific experiment: he believed all theories must be tested experimentally before being regarded as true . The work contains some of the earliest modern ideas of atoms, molecules, and chemical reaction, and marks the beginning of the history of modern chemistry . </P> <Dl> <Dt> Optics </Dt> </Dl> <P> Important work was done in the field of optics . Johannes Kepler published Astronomiae Pars Optica (The Optical Part of Astronomy) in 1604 . In it, he described the inverse - square law governing the intensity of light, reflection by flat and curved mirrors, and principles of pinhole cameras, as well as the astronomical implications of optics such as parallax and the apparent sizes of heavenly bodies . Astronomiae Pars Optica is generally recognized as the foundation of modern optics (though the law of refraction is conspicuously absent). </P> <P> Willebrord Snellius (1580--1626) found the mathematical law of refraction, now known as Snell's law, in 1621 . Subsequently René Descartes (1596--1650) showed, by using geometric construction and the law of refraction (also known as Descartes' law), that the angular radius of a rainbow is 42 ° (i.e. the angle subtended at the eye by the edge of the rainbow and the rainbow's centre is 42 °). He also independently discovered the law of reflection, and his essay on optics was the first published mention of this law . </P>

How was the new scientific knowledge spread in the seventeenth century