232 PROGRESS OF SCIENCE. 



and repulsion manifested between currents and currents, and 

 between currents and magnets. His fundamental law is 

 that " Two currents flowing in the same direction attract 

 each other ; two currents flowing in opposite directions repel 

 each other" He may be said to have been the first to prove 

 electricity to be a motive power. This motive power, applied 

 to machinery which requires enormous action, is as yet less 

 serviceable than steam; but when a comparatively small 

 force with great velocity and regularity of motion is required, 

 it is superior to all other means. It is, moreover, susceptible 

 of a great variety of applications in this respect as the 

 electric cars and railroads already in existence in America 

 and England conclusively prove. Tesla's experiments will 

 certainly lead to immense development. Ampere propounded 

 a celebrated THEORY OF MAGNETISM, according to which 

 magnetic phenomena would be caused, not by the existence 

 of two fluids, but by the existence of a closed electric current 

 in each individual molecule of a magnetic substance. He 

 also suggested that since an electric current turns metals 

 into magnets, the electric currents which flow round the 

 earth from East to West may turn our globe, which is partly 

 metallic, into a great magnet. If this be absolutely proved, 

 the view of Gilbert will be substantiated. 



17771851. Oersted invented the PIEZOMETER for 

 measuring the compressibility of liquids; discovered ELECTRO- 

 MAGNETISM, one of the most promising principles in modern 

 science (1820); showed the DISSIMILARITY OF MAGNETISM 

 and electricity by experiments which distinctly demonstrated 

 the action of the one fluid upon the other, for he found an 

 electric current passing near a magnetic needle made the 

 latter turn and lie across the path of the current. This 

 discovery of the directive action that a fixed current exerts 

 at a distance and which thus connected magnetism and 

 electricity became in the hands of Ampere as we have seen, 

 and in the hands of Faraday as we shall see, the root of a 

 new branch in physics. 



1778 1850. Gay-Lussac invented a portable barometer, 

 also an ALCOHOLOMETER, the CHRONOMETER, the ALKALI- 

 METER ; made important discoveries in moisture, atmosphere, 



