GALILEO AND THE OPTIC TUBE 201 



came to Galileo's ears. Mark that he was then long past the 

 age at which great inventions are usually made. He was then 

 forty-six. But his youthful enthusiasm, energy, resourcefulness, 

 were not gone. He travelled back to Padua from Venice, 

 where he had heard the story, and sat up all night thinking 

 about it. He had mastered all the physical knowledge of his 

 time. Kepler had written a book about optics, which he had 

 doubtless read. By morning his invention was complete. A 

 piece of old pipe served him for a tube, a pair of spectacles 

 glasses for lenses. His device was not that of the Dutchman 

 at all, and though it would only magnify three diameters, it 

 did not invert the image. He took his invention back to Venice, 

 and all the senators and distinguished men of the place had a 

 look. It made a big sensation, and Galileo enjoyed it to the 

 full. Immediately they doubled his salary, and made him a 

 professor for life. Then he set to work grinding bigger and 

 better lenses. Soon he had a telescope, the first real telescope 

 ever made, one^ that was capable of magnifying thirty-two 

 diameters ; and with that he was off in the starry ways, reach- 

 ing into depths of space no man had ever reached before, and 

 bringing back such marvels that the world was in amaze. 



This is in the year 1609, the same year that Kepler, all 

 in ignorance of the impending discovery, had completed and 

 sent forth his New Astronomy or Celestial Physics. It is just 

 sixty-six years since Coppernicus' book had come from the press. 

 How the patient old Polish canon would have stared if only 

 he might have had a look along with the Venetian senators ! 

 Could he perchance have written then so calmly, with such 

 even pulses, of the things he would have seen ? Galileo could 

 not. He is in a fever of excitement. Time will not run half 

 slowly enough to make all the discoveries he sees within his 

 grasp ; and he is making them, coining them, as Americans 

 would say. He starts what is near to a newspaper to publish 

 them to the world. 



Reflect that this telescope of thirty-two diameters is the 

 best he ever had no better than a good ship's glass now. But 

 what a flood of light it sheds ! Almost at the very first the 

 moons of Jupiter are disclosed, four of them, turning round 

 about the larger planet. This, too, is not in the books. It is 

 disturbing, upsetting. Had not Aristotle taught that the 

 number of the planets is seven, and could Aristotle lie ? But 



