CHAPTER V. Galileo

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.

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.

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.

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.

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.

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.

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.

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!

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.