When Newton's laws were applied to the paths of the moons of
Jupiter, it was noticed that the moons were a few minutes ahead of
time at that time of year when Jupiter was nearest to the earth
and a few minutes behind time when Jupiter was farthest from the
earth. Olaus Roemer, a Danish astronomer, postulated that
Jupiter's eclipses of its moons lasted seconds longer the farther
away Jupiter was from the earth because it took their light longer
to reach the earth. He concluded that light does not travel
instantaneously, but at a certain speed, which he calculated in
1676.
In 1668, Christian Huygens formulated the law of conservation of
momentum [mass times velocity], which held that when objects
collide, they may each change direction, but the sum of all their
velocities will remain the same. Huygens also recognized the
conservation of what was later called "kinetic energy", which is
associated with movement. In 1690, he posited the theory that
light consists of a series of waves. It states that all points of
a wave front of light in a vacuum may be regarded as new sources
of wavelets that expand in every direction at a rate depending on
their velocities. He thought this a better explanation of bending
and interference of light than Newton's particle theory.
In 1661, Robert Boyle, called the father of modern chemistry,
defined an element as a substance that cannot be further
decomposed and distinguished it from a mixture, which is easily
separable, and a compound, which is not easily separable.
Pages:
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852