102 PROGRESS OF SCIENCE. 



was Torr'celli who discovered the reason to be due to the 

 pressure of the atmosphere. Galileo also established another 

 LAW OF MECHANICS of great importance in determining 

 the balance of machines, that any force that will lift a weight 

 of two pounds up one foot, will lift a weight of one pound 

 up two feet the first step towards Joule's great determina- 

 tion. He made excellent observations on sound and MUSICAL 

 NOTES viz. that the greater the number of vibrations the 

 higher the note will be. He also found the law of the 

 PENDULUM by observing that the vibrations (swings), long 

 or short, of the chandelier of the Pisa Cathedral were made 

 in equal times hence the invention of the pendulum clock 

 (by Huygens). He also found one of the laws of RADIANT 

 HEAT ; endeavoured to determine the weight of air ; observed 

 numerous phenomena regarding magnetism, gravitation, and 

 acoustics. On the last subject, he taught, like Pythagoras, 

 that SOUND IS A VIBRATION OF THE AIR " which we feel 

 when it reaches the drum of the ear." (See Newton, 

 page 219.) 



The importance of Galileo's creative works on Barology 

 cannot be exaggerated : they substantially extended natural 

 philosophy being nothing less than the opening of a whole 

 department of physics, and the creation of a new class of 

 inquiries, a valuable function of which was to develop the 

 resources of experimentation.* 



Galileo by these numerous achievements proved himself a 

 masterly MATHEMATICIAN and ASTRONOMER and a supreme 

 PHYSICIST. But, we repeat, the highest philosophical import 

 of all his discoveries was the pre-eminent fact of the per- 

 manency of natural laws. 



Closing this glorious list of great men comes Kepler, 

 the contemporary of Galileo, and in some respect his rival. 

 Kepler improved the telescope using two CONVEX LENSES 

 (instead of a concave and a convex lens as Galileo had 

 done), by which improvement the instrument was made 

 more powerful, and covered a wider span of the heavens at 

 one time. He explained the TIDES to be an effect of the 

 moon's attraction a view entertained in antiquity by 



* Comte. 



