PROGRESS IN PHYSICS IN THE NINETEENTH CENTURY. 



By Professor Mendenhall, Ph. D., D. Sc, LL. D. 



On January 7, 1610, Galileo, turning his telescope toward Jupiter, 

 was the hrst to see the beautiful system of that planet in which the 

 universe is epitonnzed. He had already studied the variegated sur- 

 face of the moon and he had seen the spots upon the sun. A little 

 later, in spite of the feeble power of his instrument, he had discovered 

 that the sun rotates upon an axis, and something- of the wonderful na- 

 ture of the planet Saturn had been revealed to him. The overwhelm- 

 ing evidence thus afforded of the truth of the hypothesis of Copernicus 

 made him its chief exponent. The time had come for man to know, 

 as he had never known or even dreamed of before, his true relation 

 to the universe of which he was so insigniiicant a part. In a single 

 year nearly all of these capital discoveries were made. It was truly 

 an era of intellectual expansion; never before and never since has 

 man's intellectual horizon enlarged with such enormous rapidity. 

 One needs little imagination to share with this ardent philosophin- the 

 enthusiasm of the moment when, because some, fearing the evidence 

 of their senses, refused to look through the slender tube, he wrote to 

 Kepler: "Oh, ray dear Kepler, how I wish we could have one hearty 

 laugh together. * * * Why are you not here? AVhat shout of 

 laughter we should have at this glorious folly ! " 



Galileo died in 1042, and in the same year Newton Avas born. When 

 21 years old he ''began to think of gravity extending to the orb of 

 the moon," and before the end of the century he had discovered and 

 established the great law of universal gravitation. Thus, at the end 

 of the seventeenth century the foundations of modern physics were in 

 place. During the eighteenth century they were much built upon ; 

 but it is the nineteenth that has witnessed not only the greatest 

 advance in detail, but the most important generalizations made since 

 the time of Galileo and Newton. 



In endeavoring to present to the intelligent but perhaps unscientific 

 reader a brief review of the accomplishments of this "wonderful 



' Copyright, 1901, l>y the Sun Printing and rul^lishing Association. Reprinted, by 

 special permission, from the Sun, New York, February 17, 1901. 



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