THE AGE OF GALILEO
Galileo and the Battle for Truth
For eighteen centuries after the time of Archimedes no inventions of
importance were made. Men sought for truth where truth could not be
found. They looked within their mouldy manuscripts and asked, "What do
the great philosophers say ought to happen?" instead of looking at
nature and asking, "What does happen?" And when a man arose who dared to
doubt the authority of the old masters and turn to nature to find out
the truth, all the weapons at the command of the old school were hurled
against him.
Let us, at this distance, blame neither the one side nor the other. The
conflict was inevitable. It was an accident of history that the brunt of
the attack fell upon a man born in Italy in 1564, and that the battle
was fought chiefly in the "Eternal City," from which centuries before
had marched the legions that conquered the world.
The boy, Galileo, who was to become the central figure of the great
conflict, was talented in many ways. In lute-playing his skill excelled
that of his father, who was one of the noted musicians of his day. His
skill in drawing was such that noted artists submitted their work to
him for criticism. He wrote essays on the works of Dante and other
classical writers. He amused his boy companions by constructing toy
machines which, though ingenious, did not always work.
His preference was for mechanics, but, as this subject offered little
prospect of profitable work, he took up the study of medicine in
accordance with his father's wishes.
In his eighteenth year he entered the University of Pisa. Here he found
men who refused to think for themselves, but decided every question by
referring to what the ancient philosophers said. Galileo could not
endure such slavish submission to authority. So strongly did he assert
himself that he was nicknamed "The Wrangler," and, by his wrangling, he
lost a scholarship in the university.
He neglected his medical studies and secretly studied mathematics. His
father, learning of this, consented to his becoming a mathematician.
Thus he followed his bent, though it seemed to lead directly to poverty.
The Pendulum Clock
It was while a student at the University of Pisa that he discovered a
law of pendulums which makes possible our pendulum clocks. While at his
devotions in the cathedral, he observed the swinging of the bronze lamp
which had been drawn back for lighting. Timing its swinging by means of
his pulse, the only timepiece in his possession, he found that the time
of one swing remained the same, though the length of the swing grew
smaller and smaller. This discovery led to his invention of an
instrument for physicians' use in timing the pulse. About fifty years
later he invented the pendulum clock (Fig. 2).
[Illustration: FIG. 2--GALILEO'S PENDULUM CLOCK
It had only one hand, which is not shown in the picture.]
Lack of funds compelled him to leave the university without completing
his course. He returned to the parental roof and continued his
scientific studies. The writings of Archimedes were his favorite study.
With Archimedes' famous experiment on King Hiero's crown as a
starting-point, he discovered the laws of floating bodies, which explain
why a ship or other object floats on water, and invented a balance for
weighing objects in water.
But such employment won nothing more substantial than honor and fame.
Food and clothing were needed. For two years he strove without success
to secure employment. At the end of that time he was appointed professor
of mathematics in the University of Pisa at the magnificent salary of
sixty scudi (about sixty-three dollars) per year. "But any port in a
storm; and in Galileo's needy circumstances even this wretched salary
was not to be rejected." Moreover, he could add somewhat to his income
by private tutoring.
Galileo's Experiment with Falling Shot
While teaching at the University of Pisa, he performed his famous
experiment of dropping from the top of the leaning tower two shot, one
weighing ten pounds, the other one pound. Now, according to Aristotle,
the ten-pound shot should fall in one-tenth the time required by the
one-pound shot. But the assembled company of professors and students saw
the two shot start together, fall together, and strike the ground at
the same instant, and still refused to believe their own eyes. They
continued to affirm that a weight of ten pounds would reach the ground
in a tenth of the time taken by a one-pound weight, because they were
able to quote chapter and verse in which Aristotle assured them that
such is the fact. Thus Galileo made enemies of the other professors, but
for a time they could do nothing more than annoy him.
About this time Galileo incurred the wrath of the Grand Duke of Tuscany,
from whom he had received his appointment. He was commissioned to
examine a machine invented by a nephew of the Grand Duke for the purpose
of cleaning harbors. Galileo plainly said that the machine was
worthless. It was tried, and his opinion proved true. But like the kings
of olden time who killed the bearer of evil tidings even though the
tidings were true, his enemies made his position so unpleasant that he
resigned.
He had neither employment nor money. His father's death occurring about
this time, threw upon him the care of a mother, a worthless brother, and
two sisters. In his distress he sought help from a friend, and secured
an appointment as professor of mathematics in the University of Padua.
His salary was one hundred and eighty florins (about ninety-five
dollars), while other professors received more than ten times as much.
While at Padua, Galileo was busy inventing. He invented the sector,
which is to be found in most cases of mathematical instruments and is
used in certain kinds of drawing. He also invented an air thermometer
(Fig. 3), the first instrument for measuring temperature.
[Illustration: FIG. 3--AN AIR THERMOMETER
When the air in the bulb grows cooler it contracts, and the air
outside forces the Water up the tube. When the air in the bulb grows
warmer it expands and forces the water down in the tube.]
In 1604 there appeared a new star of great brilliancy. It continued to
shine with varying brightness for eighteen months, and then vanished.
This was a strange event, and Galileo made use of it. He proved that the
new star must lie among the most distant of the heavenly bodies, and
this fact did not agree with Aristotle's view that the heavens are
perfect, and therefore never change. A heated controversy followed, and
Galileo came out boldly in favor of the theory that the earth revolves
about the sun, the prevailing notion then being that the earth does not
move, but that the sun and other heavenly bodies revolve around it.
The Telescope
In 1609 Galileo learned of a discovery that was to be of great value to
the world, but a source of untold trouble to himself. An apprentice of a
Dutch optician, while playing with spectacle lenses, chanced to observe
that if two of the lenses were placed in a certain position objects seen
through them appeared much nearer. Galileo, learning of this, set to
work to construct a spy-glass, applying his knowledge of light. In one
day he had constructed such an instrument, in which he used two lenses
like the lenses of the modern opera-glass. Thus, while the Dutchman's
discovery was by accident, Galileo's was by reasoning, and was the more
fruitful, as we shall see.
Galileo continued improving his telescope until he had made one which
would magnify thirty times. He was the first to apply the telescope to
the study of the heavenly bodies. The most startling of his discoveries
was that of the moons of the planet Jupiter, which he called new
planets.
This aroused the fury of his enemies, who ridiculed the idea of there
being new planets; "for," they said, "to see these planets they must
first be put inside the telescope." The excitement was intense. Poets
chanted the praise of Galileo. A public fête was held in his honor. One
of his pupils was imprisoned in the tower of San Marco, where he had
gone to make observations with his telescope, and could not escape until
the crowd had satisfied their curiosity. Some of the philosophers
refused to look lest they should see and be convinced.
Galileo's Struggle
His enemies sought to steal from him the honor of his discoveries. Some
claimed to have made the discoveries before Galileo did. Others claimed
that his discoveries were false, that their only use was to gratify
Galileo's vanity and thirst for gold. In these trying times the
friendship of the great astronomer Kepler warded off some of the most
exasperating attacks.
Galileo's fame spread throughout Europe. Students came in great numbers,
so that he had little leisure left for his own studies. He therefore
decided to leave Padua, and secured an appointment as mathematician and
philosopher to the Grand Duke of Tuscany. This appointment took him to
Florence. It was here that an incident occurred that marked the
beginning of a persecution which continued to the end of his life.
As we read the story of this conflict let us remember that it was not
primarily a conflict between the Roman Catholic Church and Galileo. It
was a conflict of principles. On the one side were arrayed those who
said that men should always believe as the ancient writers did; on the
other, those who said men should think for themselves. In the first
party were most of the university professors and others who dreaded the
introduction of new beliefs, whether in religion or science. In the
second party were Galileo and a small band of devoted followers.
At a dinner at the table of the Grand Duke in Pisa the conversation
turned on the moons of Jupiter. Some praised Galileo. Others condemned
him, saying that the Holy Scriptures were opposed to his theory of the
motion of the earth. A friend reported the incident to Galileo, and he
replied to the arguments of his opponents in a letter which was made
public. No doubt the sting of his sarcasm made his enemies more bitter.
He admitted that the Scriptures cannot lie or err, but this, he said,
does not hold good of those who attempt to explain the Scriptures. In
another letter, he quoted with approval a saying of Cardinal Baronius,
"The Holy Spirit intended to teach us in the Bible how to go to Heaven,
not how the heavens go."
The first shot had been fired. The battle was on, and the Church,
because it possessed the most powerful weapons of attack, was used by
the combined forces to break the power of Galileo's reasoning. He went
to Rome to make his defence, but was commanded by the Holy Office not to
hold or teach that the sun is immovable, and that the earth moves about
the sun.
During another visit to Rome there was shown to Galileo an instrument
which, it was said, would show a flea as large as a cricket. Galileo
recalled that some years before he had so arranged a telescope that he
had seen flies which he said looked as big as a lamb, and were covered
all over with hair. This was the first microscope. Galileo quickly
improved the instrument, and soon his microscopes were in great demand.
In violation of the decree of the Church, to which he had submitted, he
published his most famous work in which he defended the theory that the
earth moves about the sun. The book was the outcome of his life-work,
but the Church believed it dangerous. He was summoned to Rome. Confined
to a sick-bed, he pleaded for delay, which was granted. Before he
recovered, however, the summons was made imperative. He must go to Rome,
or be carried in irons. He went in a litter, carried by servants of the
Grand Duke. In Rome he was to appear before the Inquisition. There he
was treated with a consideration never before accorded to a prisoner of
the Inquisition. Nor was he subjected to torture, as has been stated by
some. He was found guilty of teaching the doctrine that the sun does not
move, and that the earth moves about the sun. He was compelled to
recant, and sentenced to the prison of the Holy Office and, by way of
penance, to repeat once a week for three years the seven penitential
Psalms.
He yielded without reserve to the decree of the Inquisition, renounced
his "errors and heresies," and, with his hand on the Bible, took oath
never again to teach the forbidden doctrine.
And now, though a shattered old man of seventy-four, enjoined to
silence on the chief results of his life-work, nothing could quench his
devotion to science. In these last years, he published a new book which,
with his earlier work, entitles him to be regarded as the founder of the
science of mechanics.
In his study of machines Galileo found that no machine will do work of
itself. Whenever a machine is at work, a man or a horse, or some other
power, is at work upon the machine. In no case will a machine do work
without receiving an equal amount of work.
Torricelli and the Barometer
Galileo had a pump which he found would not work when the water was
thirty-five feet below the valve. He thought the pump was injured, and
sent for the maker. The maker assured him that no pump would do better.
This led Torricelli, one of Galileo's pupils, to the discovery of the
barometer. Men had said that water rises in a pump because nature abhors
a vacuum. Torricelli believed that air-pressure and not nature's "horror
of a vacuum" is the cause of water rising in a pump. He invented the
barometer to measure air-pressure.
The first barometer was a glass tube filled with quick-silver or mercury
(Fig. 4). The tube was closed at the upper end, and the lower end,
which was open, dipped in a dish of mercury. He allowed the tube to
stand, and saw that the height of the mercury changed. This he believed
was because the air-pressure changed. Wind, Torricelli said, is caused
by a difference of air-pressure, which is due to unequal heating of the
air. For this reason a cool breeze blows from the mountain top to the
heated valley, or from sea to land on a summer day.
[Illustration: FIG. 4--TORRICELLI'S EXPERIMENT]
Otto Von Guericke and the Air-Pump
About this time a German burgomaster, Otto von Guericke, of Magdeburg,
was performing experiments on air-pressure. The Thirty Years' War had
been raging for thirteen years. The Swedish King, Gustavus Adolphus, had
landed in Germany, and was winning victory after victory over the
imperial troops. Magdeburg had entered into an alliance with the Swedish
King, by which he was granted free passage through the city, while, on
the other hand, he promised protection to the city.
The imperial army under Tilly and Pappenheim laid siege to the city. On
the one side there was hope that Gustavus would arrive in time to effect
a rescue; on the other, a determination to conquer before such aid could
arrive. While Gustavus was on his way to the rescue, Magdeburg was taken
by storm, and the most horrible scene of the Thirty Years' War was
enacted. Tilly gave up the city to plunder, and his soldiers without
mercy killed men, women, and children. In the midst of the scene of
carnage the city was set on fire, and soon the horrors of fire were
added to the horrors of the sword. In less than twelve hours twenty
thousand people perished.
Guericke's house and family were saved, but the sufferings of the city
were not yet ended. In five years the enemy was again before the walls,
and Magdeburg, then in the possession of the Swedes, was compelled to
yield to the combined Saxon and imperial troops. Guericke entered the
service of Saxony, and was again made mayor of the city.
In the midst of these scenes of war, he found time to continue his
studies. He made the first air-pump, and with it performed experiments
which led to some very important results.
The experiments which Guericke made with his air-pump aroused the
attention of the princes, and especially Emperor Ferdinand. Guericke was
called to perform his experiments before the Emperor. The most striking
of these experiments he performed with two hollow copper hemispheres
about a foot in diameter, fitted closely together. When the air was
pumped out, sixteen horses were barely able to pull the hemispheres
apart, though, when air was admitted, they fell apart of their own
weight.
Another experiment which astonished his audience was performed with the
cylinder of a large pump (Fig. 5). A rope was tied to the piston. This
rope was passed over a pulley, and a large number of men applied their
strength to the rope to hold the piston in place. When the air was taken
out of the cylinder, the piston was forced down by air-pressure, and the
men were lifted violently from the ground. This experiment, as we shall
see, was of great importance in the invention of the steam-engine.
[Illustration: FIG. 5--GUERICKE'S AIR-PUMP
Men lifted from the ground by air-pressure.]
Guericke's study of air-pressure led him to make a water barometer (Fig.
6). This consisted of a glass tube about thirty feet long dipping into a
dish of water. The tube was filled with water, and the top projected
above the roof of the house. On the water in the tube he placed a wooden
image of a man. In fair weather the image would be seen above the
housetop. On the approach of a storm the image would drop out of sight.
This led his superstitious neighbors to accuse him of being in league
with Satan.
[Illustration: FIG. 6--GUERICKE'S WATER BAROMETER
In fair weather the image appeared above the housetop. When a storm
was approaching the image dropped below the roof into the house.]
The first electrical machine was made by Guericke. This was simply a
globe of sulphur turning on a wooden axle. He observed that when the dry
hand was held against the revolving globe, the globe would attract bits
of paper and other light objects.
Robert Boyle and the Pressure of Air and Steam
Robert Boyle, in England, improved the air-pump and performed many new
and interesting experiments with it. One of his experiments was to make
water boil by means of an air-pump without applying heat. It is now well
known that water when boiling on a high mountain is not so hot as when
boiling down in the valley. This is because the air-pressure is less on
the mountain top than in the valley. By using an air-pump to remove the
air-pressure, water may be made to boil when it is still quite cold to
the hand.
Boyle compared the action of air under pressure to a steel spring. The
"spring" of the air is evident to us in the pneumatic tire of the
bicycle or automobile. Boyle found that the more air is compressed the
greater is its pressure or "spring," and that steam as it expands
exerts less and less pressure. This is important in the steam-engine.
Pascal and the Hydraulic Press
It was Blaise Pascal, a Frenchman, who proved beyond the possibility of
a doubt that air-pressure supports the mercury in a barometer, and lifts
the water in a pump (Fig. 7). He had two mercury barometers exactly
alike set up at the foot of a mountain. The mercury stood at the same
height in each. Then one barometer was left at the foot of the mountain,
and the other was carried to the summit, about three thousand feet high.
The mercury in the second barometer then stood more than three inches
lower than at first. As the barometer was carried down the mountain the
mercury slowly rose until, at the foot, it stood at the same height as
at first. The party stopped about half-way down the mountain, allowing
the barometer to rest there for some time, and observing it carefully.
They found that the mercury stood about an inch and a half higher than
at the foot of the mountain. During all this time the height of the
mercury in the barometer which had been left at the foot of the mountain
did not change.
[Illustration: FIG. 7--A LIFT-PUMP
Air pressing down on the water in the well causes the water to rise in
the pump. The air can do this only when the plunger is at work removing
air or water and reducing the pressure inside the pump.]
It is now known that when a barometer is carried up to a height of nine
hundred feet, the mercury stands an inch lower than at the earth's
surface. For every nine hundred feet of elevation the mercury is lowered
about one inch. In this way the height of a mountain can be measured,
and a man in a balloon or an air-ship can tell at what height he is
sailing. For this purpose, however, a barometer is used that is more
easily carried than a mercury barometer.
Pascal invented the hydraulic press, a machine with which he said he
could multiply pressure to any extent, which reminds us of Archimedes'
saying that, with his own hand, he could move the earth if only he had a
place to stand. Pascal could so arrange his machine that a man pressing
with a force of a hundred pounds on the handle could produce a pressure
of many tons. In fact, a man can so arrange this machine that he can
lift any weight whatever (Fig. 8).
[Illustration: FIG. 8--A SIMPLE HYDRAULIC PRESS
A one-pound weight holds up a hundred pounds.]
The hydraulic press has two cylinders. One cylinder must be larger than
the other. The two cylinders are filled with a liquid, as water or oil,
and are connected by a tube so that the liquid can flow from one
cylinder into the other. There is a tightly fitting piston in each
cylinder. If one piston has an area of one square inch, and the other
has an area of one hundred square inches, then every pound of pressure
on the small piston causes a hundred pounds of pressure on the large
piston. A hundred pounds on the small piston would lift a weight of ten
thousand pounds on the large piston. But we can see that the large
piston cannot move as fast as the small one does. Though we can lift a
very heavy weight with this machine, we must expect this heavy weight to
move slowly. There must be a loss in speed to make up for the gain in
the weight lifted (Fig. 9). An hydraulic press with belt-driven pump is
illustrated in Fig. 10.
[Illustration: FIG. 9--HOW AN HYDRAULIC PRESS WORKS
One man with the machine can exert as much pressure as a hundred men
could without the machine. The arrows show the direction in which the
liquid is forced by the action of the plunger _p_. The large piston _P_
is forced up, thus compressing the paper.]
[Illustration: FIG. 10--AN HYDRAULIC PRESS WITH BELT-DRIVEN PUMP]
Newton
Sir Isaac Newton as a boy did not show any unusual talent. In school he
was backward and inattentive for a number of years, until one day the
boy above him in class gave him a kick in the stomach. This roused him
and, to avenge the insult, he applied himself to study and quickly
passed above his offending classmate. His strong spirit was aroused, and
he soon took up his position at the head of his class.
It was his delight to invent amusements for his classmates. He made
paper kites, and carefully thought out the best shape for a kite and the
number of points to which to attach the string. He would attach paper
lanterns to these kites and fly them on dark nights, to the delight of
his companions and the dismay of the superstitious country people, who
mistook them for comets portending some great calamity. He made a toy
mill to be run by a mouse, which he called the miller; a mechanical
carriage, run by a handle worked by the person inside, a water-clock,
the hand of which was turned by a piece of wood which fell or rose by
the action of dropping water.
At the age of fifteen, his mother, then a widow, removed him from school
to take charge of the family estate. But the farm was not to his liking.
The sheep went astray, and the cattle trod down the corn while he was
perusing a book or working with some machine of his own construction.
His mother wisely permitted him to return to school. After completing
the course in the village school he entered Trinity College, Cambridge.
Gravitation
It was in the year following his graduation from Cambridge that he made
his greatest discovery--that of the law of gravitation. A plague had
broken out in Cambridge, to escape which Newton had retired to his
estate at Woolsthorpe. Here he was sitting one day alone in the garden
thinking of the wonderful power which causes all bodies to fall toward
the earth. The same power, he thought, which causes an apple to fall to
the ground causes bodies to fall on the tops of the highest mountains
and in the deepest mines. May it not extend farther than the tops of the
mountains? May it not extend even as far as the moon? And, if it does,
is not this power alone able to hold the moon in its orbit, as it bends
into a curve a stone thrown from the hand?
There followed a long calculation requiring years to complete. Seeing
that the results were likely to prove his theory of gravitation, he was
so overcome that he could not finish the work. When this was done by one
of his friends, it was found that Newton's thought was correct--that the
force of gravitation which causes bodies to fall at the earth's surface
is the same as the force which holds the moon in its orbit. As the earth
and moon attract each other, so every star and planet attracts every
other star and planet, and this attraction is gravitation.
Colors in Sunlight
About the same time that he made his first discoveries regarding
gravitation, he took up the study of light with a view to improving the
construction of telescopes. His first experiment was to admit sunlight
into a darkened room through a circular hole in the shutter, and allow
this beam of light to pass through a glass prism to a white screen
beyond. He expected to see a round spot of light, but to his surprise
the light was drawn out into a band of brilliant colors.
He found that the light which comes from the sun is not a simple thing,
but is composed of colors, and these colors were separated by the glass
prism. In the same way the colors of sunlight are separated by raindrops
to form a rainbow. The colors may be again mingled together by passing
them through a second prism. They will then form a white light.
Suppose that the light of the sun were not composed of different colors,
that all parts of white light were alike, then there would be no colors
in nature. All the trees and flowers would have a dull, leaden hue, and
the human countenance would have the appearance of a pencil-sketch or a
photographic picture. The rainbow itself would dwindle into a narrow
arch of white light; the sun would shine through a gray sky, and the
beauty of the setting sun would be replaced by the gray of twilight
(Fig. 11).
[Illustration: FIG. 11--NEWTON'S EXPERIMENT WITH THE PRISM
Sunlight separated into the colors of the rainbow. The seven colors
are: violet, indigo, blue, green, yellow, orange, red.]
One of Newton's inventions was a reflecting telescope--that is, a
telescope in which a curved mirror was used in place of a lens. He made
such a telescope only six inches long, which would magnify forty times.
Newton was a member of the Convention Parliament, which declared James
II. to be no longer King of England and tendered the crown to William
and Mary. He was made a knight by Queen Anne in 1705.
His knowledge of chemistry was used in the service of his country when
he was Master of the Mint. It was his duty to superintend the recoining
of the money of England, which had been debased by dishonest officials
at the mint. He did his work without fear or favor.
Once a bribe of £6000 ($30,000) was offered him. He refused it,
whereupon the agent who made the offer said to him that it came from a
great duchess. Newton replied: "Tell the lady that if she were here
herself, and had made me this offer, I would have desired her to go out
of my house; and so I desire you, or you shall be turned out."
Although Newton's discoveries in the world of thought were among the
greatest ever made by man, he regarded them as insignificant compared
with the truth yet undiscovered. He said of himself: "I do not know what
I may appear to the world, but to myself I seem to have been only like a
boy playing on the sea-shore and diverting myself in now and then
finding a smoother pebble or a prettier shell than the ordinary, whilst
the great ocean of truth lay all undiscovered before me."