374 



SCIENTIFIC THOUGHT. 



the actions of large masses and complicated systems of 

 bodies by a process of summation from the interaction of 

 units placed in the simplest relation that of two and 

 two, pushing or pulling each other in a straight line. 

 Now, in consequence of the great distances at which we 

 are placed from the heavenly bodies, these appear to us 

 as mere points, and the observation of their movements, 

 their orbits, and their periods enabled astronomers like 

 Kepler, and mathematicians like Newton, to gain by mere 

 observation and subsequent calculation an idea of the 

 elementary rule which masses, considered to be concen- 

 trated in points, follow in their motion in a connected 

 system. The next step was to see how these elementary 

 actions would add up in cases where the dimensions of 

 the moving bodies were not vanishingly small in com- 

 parison with their distances. The infinitesimal methods, 

 invented in the age of Newton, and developed by him 

 and others into a special calculus, came to the aid of 

 mathematicians, and enabled them to calculate from 

 elementary data the motions and phenomena of extended 

 bodies and systems of bodies. These could afterwards 

 be actually measured, thereby confirming the elementary 

 formulae and assumptions which had formed the basis of 

 those calculations. As already remarked, this process 



other bodies, which are not con- 

 ductors, there exist, not currents, 

 but only vibrations, which may in 

 future be observed by the methods 

 indicated above. Further, I need 

 only point to Faraday's recent dis- 

 covery of the influence of electric 

 currents on the vibrations of light, 

 which makes it probable that the 

 all-pervading neutral electric medi- 

 um itself constitutes the all-pervad- 



ing ether which contains and pro- 

 pagates luminous vibrations, or at 

 least that the two are so intimately 

 connected that the observation of 

 luminous vibrations may afford some 

 information regarding the proper- 

 ties of the neutral electric medium." 

 He then refers to Ampere's own 

 suggestion in this direction. (' Elec- 

 trodynamische Maasbestimmungen,' 

 Part I., p. 169.) 



