The Science Book

SCIENTIFIC REVOLUTION 69

Sun, the perihelion of its orbit
would stay in the same place.
However all the planets in our solar
system affect each other, so the
perihelia precess (rotate) around
the Sun. Like all the other planets,
Mercury’s perihelion precesses,
but the precession cannot be
completely accounted for using
Newton’s equations. This was
recognized as a problem in 1859.
More than 50 years later, Einstein’s
Theory of General Relativity
described gravity as an effect of
the curvature of space-time, and
calculations based on this theory
do account for the observed
precession of Mercury’s orbit,
as well as other observations not
linked to Newton’s laws.

Newton’s laws today
Newton’s laws form the basis of
what is referred to as “classical
mechanics”—a set of equations
used to calculate the effects of
forces and motion. Although these
laws have been superseded by
equations based on Einstein’s
theories of relativity, the two sets
of laws agree as long as any motion

involved is small compared to

the speed of light. So for the

calculations involved in designing

airplanes or cars, or figuring out

how strong the components of

a skyscraper need to be, the

equations of classical mechanics

are both accurate enough and

much simpler to use. Newtonian

mechanics, while it may not strictly

be correct, is still widely used. ■

Nature and nature’s laws lay

hid in night; God said “Let

Newton be” and all was light.

Alexander Pope

Isaac Newton

Born on Christmas Day in

1642, Isaac Newton attended

school in Grantham, before

studying at Trinity College,

Cambridge, where he

graduated in 1665. During

his life, Newton was variously

Professor of Mathematics at

Cambridge, Master of the

Royal Mint, Member of

Parliament for Cambridge

University, and President of

the Royal Society. Besides

his dispute with Hooke,

Newton became involved

in a feud with German

mathematician Gottfried

Leibnitz over priority in the

development of calculus.

In addition to his

scientific work, Newton

spent much time in alchemical

investigations and Biblical

interpretation. A devout but

unorthodox Christian, he

successfully managed to

avoid being ordained as a

priest, which was normally

a requirement for some of

the offices he held.

Key works

1684 On the Motion of Bodies

in an Orbit

1687 Philosophiae Naturalis

Principia Mathematica

1704 Opticks

The precession (change in the

rotational axis) of the orbit of Mercury

was the first phenomenon that could

not be explained by Newton’s laws.