THE PRINCIPLES OF SCIENCE 185 



Instead we constitute light a "something" which travels from source 

 to destination, thus achieving continuity of connection in space as 

 well as continuity of existence in time. 



Some half-century ago quantum phenomena began increasingly to 

 breach the conception of continuity so long taken for granted. Secure 

 in that conception, we reject out of hand the suj^position of some 

 early societies that the sun is annihilated at dusk and reborn at dawn; 

 but Bohr's conception of "quantum jumps" may be held to imply that 

 an electron disappears here and reappears there without any inter- 

 mediary "existence." As a matter of record this denial of continuity 

 proved highly oflFensive to many physicists of the early 20th century, 

 and even today a few are deeply disturbed by what Schrodinger 

 called "the nightmare that physical events consist in continual se- 

 quences of little fits and jerks." That this should seem a "nightmare" 

 is testimony to the strength of the abiding human concern with con- 

 tinuity. Indeed this nightmare parallels ( perhaps even in futility? ) a 

 problem that, in a very diflFerent age, agitated the scholastics: when 

 angels move from place to place, do they pass through the intermedi- 

 ate space? In any case, whatever the ultimate outcome of attempts 

 to dispel Schrodinger 's nightmare, quantum mechanics still preserves 

 absolutely intact those major elements of continuity embodied in the 

 various conservation laws. 



Energy. For Anaximenes "motion is from eternity." Today "kinetic 

 energy" has become one measure and expression of the quantity of 

 motion. But clearly kinetic energy is not constant even for one single 

 oscillation of a simple pendulum. To maintain constancy of "energy'^ 

 we then introduce a term representing "potential energy," hypothe- 

 sizing that the sum (but not the distribution) of energies remains 

 constant. Of course, kinetic and mechanical potential energies are 

 insufficient to maintain the constancy we seek in all the cases with 

 which ultimately we must deal. In the 19th century, conservation of 

 energy required the postulation of multiple species of interconvert- 

 ible energies— thermal, chemical, electric, magnetic, radiant, etc. At 

 the beginning of the 20th century, the apparently limitless evolution 

 of heat by the then-newly-discovered radioactive elements posed a 

 problem resolved only with the conception of an interconvertibility 

 of mass and energy— mass becoming itself a species of energy. Little 

 more than a quarter of a century ago, what seemed a genuine crisis 

 was averted only with the postulation of the neutrino. A purely ad 



