I. The Nature of the Scientific Method 



The learned physicist and the man in the street were standing 

 together on the threshold about to enter a room. 



The man in the street moved forward without trouble, planted 

 his foot on a solid unyielding plank at rest before him, and 

 entered. 



The physicist was faced with an intricate problem. To make 

 any movement he must shove against the atmosphere, which 

 presses with a force of fourteen pounds on every square inch of 

 his body. He must land on a plank travelling at twenty miles a 

 second round the sun — a fraction of a second earlier or later the 

 plank would be miles away from the chosen spot. He must do 

 this whilst hanging from a round planet head outward into space, 

 and with a wind of ether blowing at no one knows how many 

 miles a second through every interstice of his body. He reflects 

 too that the plank is not what it appears to be — a continuous support 

 for his weight. The plank is mostly emptiness ; very sparsely 

 scattered in that emptiness are myriads of electric charges dashing 

 about at great speeds but occupying at any moment less than a 

 billionth part of the volume which the plank seems to fill con- 

 tinuously. It is like stepping on a swarm of flies. Will he not 

 slip through ? No, if he makes the venture, he falls for an instant 

 till an electron hits him and gives a boost up again ; he falls again, 

 and is knocked upwards by another electron ; and so on. The 

 net result is that he neither slips through the swarm nor is bom- 

 barded up to the ceiling, but is kept about steady in this shuttlecock 

 fashion. Or rather, it is not certain but highly probable that he 

 remains steady ; and if, unfortunately, he should sink through the 

 floor or hit the ceiling, the occurrence would not be a violation of 

 the laws of nature but a rare coincidence. 



By careful calculation of these and other conditions the 

 physicist may reach a solution of the problem of entering a room ; 

 and, if he is fortunate enough to avoid mathematical blunders, he 

 will prove satisfactorily that the feat can be accomplished in the 

 manner already adopted by his ignorant companion. Happily 

 even a learned physicist has usually some sense of proportion ; and 



