" From the point of view of the physicist, a theory of matter is a 

 policy rather than a creed; its object is to connect or co-ordinate 

 apparently diverse phenomena, and above all to suggest, stimu- 

 late and direct experiment. It ought to furnish a compass which, 

 if followed, will lead the observer further and further into pre- 

 viously unexplored regions. Whether these regions will be barren 

 or fertile experience alone will decide; but, at any rate, one who 

 is guided in this way will travel onward in a definite direction, and 

 will not wander aimlessly to and fro." J. J. Thomson, "The 

 Corpuscular Theory of Matter," 



