Advances in Physical Science. 21 



The Great Problem. 



The problem of the great physical forces 

 has engaged the profoundest attention of 

 mankind from the earliest historic period 

 down to the present time, yet it remains 

 practically unsolved. 



Before the Christian era the opinion was 

 entertained that all of the phenomena of 

 nature might be reduced to one principle of 

 explanation ; that there was more than a con- 

 nection between the imponderable agents 

 more than a relationship even, that there 

 was an actual identity. 



No substantial progress was thereafter 

 made in the direction of verifying this theory 

 until along into the present century, when the 

 development of electrical science presented a 

 tangible basis for successful investigation. 



The correlation of nearly all of those for- 

 ces is now assured, leaving little to be added 

 besides gravity to complete the unity. Yet 

 notwithstanding the satisfactory progress 

 which has been made in solving the grand 

 problem of their correlation, little has been 

 learned of their intimate nature, and the 

 method of their operation. This is due, in 

 the highest degree, to certain theories which 



