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 Xewton, 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- ing ether which contains and pro- 



ductors, there exist, not currents, pagates luminous vibrations, or at 



but only vibrations, which may in ! least that the two are so intimately 



future be observed by the methods connected that the observation of 



indicated above. Further, I need 



luminous vibrations mav afford some 



only point to Faraday's recent dis- information regarding the proper- 



covery of the influence of electric ' ties of the noutral electric medium." 



currents on the vibrations of light, I He then refers to Ampere's own 



which makes it probable that the i suggestion in this direction. ('Elec- 



all-prevadiug neutral electric medi- trodynamische Maasbestimmungen,' 



um itself constitutes the all-prevad- Part I., p. 169.) 



