ESSAYS 313 



train him up for the medical profession. It is recorded that after leaving school 

 he accidentally went to listen to a lecture on mathematics, and was so much 

 attracted that he devoted his leisure time to a private study of the subject. 

 Watching the swinging of a lamp suspended by a long rope in the dome of Pisa, 

 he compared the time of its oscillation with the beat of his pulse. He was then a 

 medical student, and possibly he only intended to find a scientific method of 

 measuring changes in the rate of beating of the pulse. Be this as it may, he 

 discovered that the time of swing was the same whether the lamp swung through 

 a large or small arc, and had sufficient insight to recognise that this was a funda- 

 mental discovery. He was then nineteen years old, and this event turned his 

 mind to the study of dynamics. At the age of twenty-five he obtained a Professor- 

 ship of Mathematics at a salary of ^12 a year. He came into contact with the 

 scholastic philosophers, because he proved by experiment that, contrary to the 

 orthodox views, heavy and light bodies acquired the same velocity in falling. 



Galileo was a fighter by temperament, and fearless — up to a certain point. He 

 made enemies in quantity, but he also had the power of gaining staunch friends, 

 who remained true to him through life. I cannot here enter into the astonishingly 

 successful progress of his dynamical work, but pass on at once to the turning- 

 point which led to the crisis in his life, and marks the beginning of modern 

 science. 



The faith in the old Aristotelian doctrine, which Roger Bacon did not succeed 

 in weakening by powerful reasoning, was profoundly shaken by a few nights' 

 visual observation, and henceforth survived only in a few strongholds of reactionary 

 prejudice. 



Galileo, applying his newly-constructed telescope to Jupiter, had discovered 

 four moons revolving round that body. The appeal was to imagination rather 

 than to logic : the earth has a moon ; Jupiter is a planet and has moons ; therefore 

 the earth is a planet. The argument put in this way does not satisfy the strict 

 rules of correct reasoning ; but it touches the chord of human sympathy. If it be 

 accepted, the planetary system is transformed into a harmonious whole. 



Galileo's discoveries were numerous and brilliant, and he placed dynamics on 

 a solid foundation ; but he rendered a greater service to mankind when he taught 

 the worker that science was not the monopoly of the philosopher, the monk, or the 

 impostor, but belonged to the man of intellect in every rank of life. Herein lies 

 his claim to be called the founder of our present science. Latin was then the 

 international language ; Galileo preferred to write in Italian. It was not that 

 he was unacquainted with classical literature, but he deliberately chose the 

 language of his own people because he preferred to address them rather than 

 the learned of other nations. His powers of exposition were as great as his 

 powers of reasoning, and there is little doubt that the great influence he had on 

 his generation was largely due to the vigorous manner in which he used his native 

 tongue. 



I have mentioned Darwin's work as a second example of an investigation in 

 pure science that has led to a great and lasting effect on the intellectual progress 

 of the world. Those whose memory can carry them back to the time of its 

 publication will not have forgotten the stir created by the appearance of the 

 Origin of Species. As in Galileo's case, its effect was enhanced by being placed 

 before the public in a form which allowed its general drift to be appreciated 

 by all educated men. The Copernican theory introduced harmony into the 

 planetary system, and the idea of natural selection united in a similar manner 

 the different branches of the organic world. Both with Galileo and Darwin the 



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