Forces and Atoms: The World of The Physicist

NE of the signs whereby a physicist may be known is a fondness for putting dots upon blackboards. This is not an irrational habit, but a symbolic practice. It is a symbol of his manner of regarding the world as a multitude incredibly enormous of particles incredibly small. The dots stand for the particles, and the bare regions of the blackboard for the empty spaces between them. The habit has not indeed been universal. Many a thinker has preferred to consider the world as a continuum, a solid or jelly or fluid; and we shall see that this alternative has always been very near in the background, even when the "atomists" were at their most triumphant. Let me however defer this other idea, and derive as much as possible from the notion of particles in a void. But when the dots are set down on the otherwise clean board with regions of black emptiness between, the story is far from completed. It is, in fact, only begun, for the major part is yet to be written: the account of the forces among the particles. Though these last be separated from each other by spaces apparently empty, yet they are not unconscious of each other, for each of them is subject to a force--the resultant of many forces, due to all rest. One might attach an arrow to each dot, to signify the strength and the direction of the force which acts upon it. One might draw wandering curves all over the board, to intimate at every point the direction and strength of the force which a particle would feel, were it to be at that point.