Huygens admitted that the planets and their satellites attracted each other with a force varying according to the inverse ratio of the squares of their distances, but rejected the mutual attraction of the molecules of matter, believing that they possessed gravity towards a central point only, to which they were attracted. This supposition was at variance with the Newtonian theory, which, however, was universally regarded as the correct one.
Huygens originated the theory by which it is believed that light is produced by the undulatory vibration of the ether; he also discovered polarization.
Up to this time the method adopted in the construction of clocks was not capable of producing a mechanism which measured time with sufficient accuracy to satisfy the requirements of astronomers. Huygens endeavoured to supply this want, and applied his mechanical ingenuity in constructing a clock that could be relied upon to keep accurate time. Though the pendulum motion was first adopted by Galileo, he was unable to arrange its mechanism so that it should keep up a continuous movement. The oscillation of the pendulum ceased after a time, and a fresh impulse had to be applied to set it in motion. Consequently, Galileo’s clock was of no service as a timekeeper.
Huygens overcame this difficulty by so arranging the mechanism of his clock that the balance, instead of being horizontal, was directed perpendicularly, and prolonged downwards to form a pendulum, the oscillations of which regulated the downward motion of the weight. This invention, which was highly applauded, proved to be of great service everywhere, and was especially valuable for astronomical purposes.
Huygens next directed his attention to the construction of telescopes, and displayed much skill in the grinding and polishing of lenses. He made several instruments superior in power and accuracy to any that existed previously, and with one of these made some remarkable discoveries when observing the planet Saturn.
The telescopic appearance of Saturn is one of the most beautiful in the heavens. The planet, surrounded by two brilliant rings, and accompanied by eight attendant moons, surpasses all the other orbs of the firmament as an object of interest and admiration. To the naked eye, Saturn is visible as a star of the first magnitude, and was known to the ancients as the most remote of the planets. Travelling in space at a distance of nearly one thousand millions of miles from the Sun, the planet accomplishes a revolution of its mighty orbit in twenty-nine and a half years.
Galileo was the first astronomer who directed a telescope to Saturn. He observed that the planet presented a triform appearance, and that on each side of the central globe there were two objects, in close contact with it, which caused it to assume an ovoid shape. After further observation, Galileo perceived that the lateral bodies gradually decreased in size, until they became invisible. At the expiration of a certain period of time they reappeared, and were observed to go through a certain cycle of changes. By the application of increased telescopic power it was discovered that the appendages were not of a rounded form, but appeared as two small crescents, having their concave surfaces directed towards the planet and their extremities in contact with it, resembling the manner in which the handles are attached to a cup.
These objects were observed to go through a series of periodic changes. After having become invisible, they reappeared as two luminous straight bands, projecting from each side of the planet; during the next seven or eight years they gradually opened out, and assumed a crescentic form; they afterwards began to contract, and on the expiration of a similar period, during which time they gradually decreased in size, they again became invisible. It was perceived that the appendages completed a cycle of their changes in about fifteen years.
In 1656, Huygens, with a telescope constructed by himself, was enabled to solve the enigma which for so many years baffled the efforts of the ablest astronomers. He announced his discovery in the form of a Latin cryptograph which, when deciphered, read as follows:—
‘Annulo cingitur, tenui plano, nusquam cohaerente, ad eclipticam inclinatio.’