GALILEO
THE man who is considered the greatest of all pioneers of
science was born in the year 1564 at the city of Pisa, in the north of
Italy. He first studied medicine, but after a few years he turned his
attention to Mathematics and Science, which suited him much better.
When only twenty-five years of age he was appointed for three years as
Professor of Mathematics in Pisa. He soon showed that he did not intend
to follow slavishly in the footsteps of the old masters. He lived at a
time when a new spirit of independent inquiry was beginning to be felt
in the universities of Europe.
Galileo’s most remarkable early achievement was connected with the
famous leaning tower of Pisa. That tower had been built on a weak
foundation, and after it was finished it began to lean over towards one
side, owing to the ground giving way beneath it. However, the tower did
not fall, but remained in a leaning position. It was used by Galileo in
order to prove that the old Greeks were wrong when they said that a
heavy body would fall more quickly than a light body.
[Illustration: Fig. 23.--Galileo.]
This is true, of course, when we compare a feather with a stone. But
that is due to the resistance of the air. If no air were present the
stone and the feather would fall to the ground together, and the
feather would make a little rattling noise just as if it were a piece
of wire. This, of course, could not be proved by Galileo, as he had no
means of obtaining a space free from air. But at all events he was well
able to compare the rates at which a large stone and a small stone fell.
The old Greeks had stated that large stones and small stones fall at
different rates, and nobody seems to have taken the trouble to find out
whether that is the case. Galileo did try on many occasions. He took
up a large stone in one hand and a small stone in the other hand, and
let them drop together. He found that they reached the ground at the
same instant. When he showed the experiment to his friends, they said
there was a difference in the rate at which the two stones fell, but
that the distance through which they fell was not great enough to allow
this difference to appear. To answer this objection Galileo went to the
top of the tower of Pisa. He took with him a cannon ball weighing a
hundred pounds and a shot weighing one pound. These were contained in
a box, and were dropped by overturning the box. They therefore started
together, and the people who watched the experiment also found that
they arrived at the bottom of the tower at exactly the same moment.
They seemed to hit the ground at the same time.
This famous experiment was the starting-point of a revolution.
[Illustration: Fig. 24.--The Leaning Tower of Pisa.]
The fall of those two balls marked the fall of the old system by which
the advance of science had been so long delayed. Henceforth Galileo
did not stop to consult the old masters before he tried an experiment.
Nature, he said, was always ready to answer questions. The only thing
necessary was to put the question to her in a clear and unmistakable
manner. Nature never hesitated with her answer. He therefore proceeded
during the rest of his life to question Nature constantly and
methodically. In this way he was able to discover a great number of new
laws, and his method has since been accepted as the only sure method by
which our knowledge of the structure and constitution of this world can
be extended.
Wishing to determine the speed of falling bodies more accurately,
Galileo varied the experiment in different ways. In one method, which
he used a great deal, he made spheres or balls of solid brass run down
a groove cut into a wooden board. This groove was lined with smooth
parchment, so that there should be as little resistance as possible to
the motion of the balls. He measured accurately the time at which the
balls were started and the time at which they arrived at the bottom
of the groove. These measurements would nowadays be made by means of
a watch, but at that time there were no watches except water-clocks,
such as had been used in Babylon, and, later on, in Alexandria.
Galileo measured time as best he could with the help of one of these.
He attached a small spout to the bottom of a pail of water, so that the
water ran out in a thin jet. At the instant when he started the ball on
its way down the groove he placed a little cup under the water tap, and
at the instant when the ball reached the bottom of the groove he took
the cup away.
[Illustration: Fig. 25.--A Simple Water-Clock.]
He then weighed the cup with and without the water, and so found the
amount of water that had flowed into the cup. By comparing the amounts
of water obtained in different experiments he was able to compare the
times.
His first object was to find in what way the speed of the body varied
with the distance over which it travelled, or the time during which it
was travelling. He first of all thought that the speed was proportional
to the distance travelled. He soon found, however, that when the
distance is doubled the speed at the end of the fall is not doubled. It
is less than double what it was before. This can be proved by letting
a ball roll along a very smooth surface after it has reached the bottom
of the groove. Galileo found at the end of a long set of experiments
that the speed attained by a body is exactly proportional to the time
during which it is exposed to a force capable of moving it. This
discovery was the origin of the whole science of motion. Galileo called
the speed which a body acquires in the unit of time the “acceleration”
of that body.
Galileo was the first to establish the idea of what is known in science
as Momentum. He found that the amount of motion in a body must be
judged not only by its speed, but also by the weight of the body. It
was evident to him that a heavy body moving at a certain speed is
equivalent to a number of lighter bodies moving with the same speed,
their combined weight being the same as the weight of the heavy body.
In order, therefore, to determine the amount of motion in a moving
body, it was necessary to take into account both the weight of the
body and the speed. Galileo used the word “momentum” to signify the
result obtained by multiplying together the two numbers expressing the
speed and the weight of a body. He also started the idea of centrifugal
force, or the force with which a body stretches a string when it is
swung round by the string.
But the most important work of Galileo was that which he did with the
pendulum. When still quite a young man, it happened that he was at
the cathedral at Pisa during a service. He noticed that a great lamp
suspended from the ceiling far overhead had been left swinging after it
had been lighted. He watched the lamp swinging to and fro for a long
time, and noticed that the swinging gradually diminished. But while the
amount of swinging diminished, the time of swinging appeared to remain
the same. In order to test this he counted the number of times his own
pulse would beat between one swing and the next. He had no clock or
watch in his possession, and was unable, in the circumstances, to use
such a thing as a water-clock, considering that he was supposed to be
engaged at his prayers. By counting his pulse he found that the time of
swinging remained exactly the same until the swing had quite died away.
Any ordinary young man would not have found anything very interesting
in that, but to Galileo the observation was a kind of revelation. He
thought that if he could work out a machine driven by swinging weights,
such a machine could be made to go quite steadily, and could be made
into a clock which would show the time accurately. He did contrive a
kind of counting machine by means of a pendulum which would count its
own swings, but he did not succeed in making a clock that would keep
going any length of time. He designed a clock which could be wound up
and driven by means of a weight, but this was not done until he was
very old and blind, and he could only dictate the description of the
clock to his son, and the latter did not succeed in constructing the
clock until ten years after his father’s death. Nevertheless Galileo
must be regarded as the inventor of the pendulum clock.
In the year 1609 a rumour reached Galileo which started him on an
entirely new line of discovery. He had heard that a Dutch optician had
presented to a German prince an instrument constructed in such a manner
that objects which were distant could be seen as if they were near. A
letter which he received from Paris confirmed the news, but could not
give him any information as to how the instrument was constructed.
Galileo thought about this discovery for a whole night, and in the
morning he had found out the secret of it. He took two lenses, one
of them a magnifying glass, and the other a glass which made things
smaller. The magnifying glass he fixed at one end of a leaden pipe, and
at the other end he fixed the other glass. This end he held to his eye,
and the other end he directed towards a distant object. At first he saw
nothing, but on moving the magnifying glass to and fro along the pipe,
he found the position in which distant objects appeared magnified to
three times the ordinary size. He straightway set to work to improve
the instrument, and in a short time he succeeded in constructing a
telescope which brought objects thirty times nearer and magnified their
surface a thousand times.
[Illustration: Fig. 26.--A modern Astronomical Telescope.]
Galileo went to Venice and showed it to the chiefs of the Republic. He
took them up to the highest church tower in the city, and mounted his
telescope so as to look out to sea.
He said, “Many noblemen and senators, although of great age, mounted
the steps of the highest church towers at Venice to watch the ships,
which were visible through my glass two hours before they were
seen entering the harbour.” This remarkable invention made Galileo
world-famous. The kings, princes, and learned men of the world all
wanted telescopes, and asked Galileo to make them. Such requests even
came from Holland, where the principle of the telescope had first been
discovered.
But although the great men of Europe used the telescope on many
occasions both in peace and in war, Galileo put it to a greater use.
He conceived the idea of turning it to the heavens and examining the
celestial bodies. In doing so he obtained a most surprising series of
revelations. He first of all turned it on the moon, and saw at once
that the markings on the surface of the moon were really mountains and
level plains. He could watch the shadows of the mountains grow and
diminish with the varying direction of the sun’s rays, and he could
even prove that some of the mountains were higher than others. He then
turned his telescope on the great planet Jupiter, and noticed to his
great surprise that Jupiter had near it four smaller companions which
circled round it in a few days. In fact, he found that Jupiter has four
moons where the earth has only one. This discovery was entirely opposed
to the ancient idea, then universally held, that there were only seven
planets or moving stars, namely: the Sun, the Moon, Mercury, Venus,
Mars, Jupiter, and Saturn.
On pointing the telescope to another great planet, Saturn, Galileo
found that another surprise awaited him. It looked as if the planet had
two handles, like a jug. This strange appearance was really owing to
the fact that Saturn is surrounded by a fiat ring, which being slightly
tilted gave the appearance of the two handles. This, of course, was
not known at that time to Galileo, but he certainly was the first to
observe that Saturn had a very unusual appearance.
[Illustration: Fig. 27.--The Planet Saturn and its Rings.]
Galileo next turned his telescope on the sun at a time when it was near
the horizon, and not strong enough to blind him. He observed that the
sun was not evenly bright all over its surface, but that there were
spots on it. These spots came and went, and could be seen to appear
at one edge of the sun, to move round, and to disappear at the other
edge about a fortnight later. This gave Galileo the idea that the sun
revolves on its axis.
After that, Galileo turned his attention to the planet Venus, and
found, contrary to all accepted opinions, that this glorious planet
showed phases like the moon, and was sometimes seen in the shape of a
crescent. Such appearances were not presented by Jupiter or Saturn, and
it struck Galileo that the probable explanation of this must be that
Venus revolves round the sun at a lesser distance than the earth, and
the other planets at a greater distance.
[Illustration: Fig. 28.--Photograph of the Sun on two successive days,
showing Sun-Spots and the Rotation of the Sun.]
Now at the time of Galileo the accepted opinion was that the earth
stood still, and that the sun and all the planets revolved round the
earth. This opinion the professors and philosophers of the time sought
to justify by quoting the Holy Scriptures, pointing out such a passage,
for instance, as that in which Joshua is said to have commanded the sun
to stand still. Galileo replied that the Bible was intended as a guide
in religious matters, but not as a text-book of science, and that the
only method of arriving at truth in science was by carefully observing
the phenomena and seeking for their most reasonable explanation.
However, he was faced with a strong opposition. Some of the enemies
refused to believe their eyes, saying that although the telescope was
useful in observing objects on land or sea, it was misleading when
pointed at the stars. Others refused to look through it at all.
[Illustration: Fig. 29.--The Earth in Space.]
About one of these objectors Galileo wrote to his friend Kepler,
“Oh, my dear Kepler, how I wish that we could have one hearty laugh
together!
[Illustration: Fig. 30.--Galileo’s Pendulum Clock.]
Here at Padua is the principal professor of Philosophy, whom
I have repeatedly and urgently requested to look at the moon and
planets through my glass, which he obstinately refuses to do. Why are
you not here? What shouts of laughter we should have at this glorious
folly! And to hear the professor of Philosophy at Pisa labouring before
the Grand Duke with logical arguments, as if with magical incantations
to charm the new planets out of the sky.”
At length the enemies of Galileo denounced him in Rome, and Galileo
was called before the Inquisition to answer for his strange doctrines.
The court before which he was judged decided that his doctrines were
contrary to divine revelation, and threatened him with torture if he
should continue to teach them. Galileo had no choice but to renounce
his doctrine that the earth moved round the sun, and to do penance for
having taught it. He was now seventy years old, and although he was
allowed to return to his home his useful work was nearly at an end. He
devoted the remainder of his days to Mathematics and to the invention
of the pendulum clock, as already stated.
The centuries which succeeded Galileo have fully justified him and
his teachings. The idea that the earth moved round the sun is now
completely established, and is universally accepted by all educated
people. Not only that, but science is now free to pursue its course
without regard to the errors and prejudices of the old schools of
Philosophy. It is now recognised that no artificial limits can or must
be put in the way of the march of the human intellect, and that the
increase of knowledge makes invariably for the increased happiness of
mankind.