36 Journal of the Mitchell Society [Septcmher 



him it was always six o'clock and always tea-time. Einstein goes 

 even farther than this; let me quote his own words: ''We could sub- 

 stitute for the clock a living organism enclosed in a box. Were it 

 hurled through space like the clock it would be possible for the organ- 

 ism, after a flight of whatever distance, to return to its starting point 

 practically unchanged, while an exactly similar organism which re- 

 mained motionless at the starting point might have given place to 

 new generations. For the organism in motion, time was but a moment, 

 if its speed approached the velocity of light." This statement implies 

 that not only does time depend on velocity, but that the rapidity of 

 chemical and biological processes is also a function of velocity. 



Rosalind's remark is therefore doubly true, that "Time travels 

 in divers paces with divers persons," and until the velocity 

 of each system is known (that is, the relative velocity, for we 

 can never find the absolute velocity of any system,) we cannot know 

 with whom the swift foot of Time ambles, trots, gallops, or even 

 stands still withal. One observer's now may be another observer's 

 future and a third observer's past, all at the some cosmical moment 

 of time. Two actions quite simultaneous to one observer may not be 

 simultaneous to another observer located in a different system. Again, 

 what to a stationary observer is an electrostatic field is to a moving 

 observer an electromagnetic field. 



According to Einstein and Minkowski any point relatively at rest 

 in space really traces a "world-line" or "path of adventure" parallel 

 to the time axis. The locus of a point in relative motion is a line mak- 

 ing an angle with the time axis. An observation is the crossing of 

 two or more world-lines, and we know nothing of these world-lines 

 between the points of crossing with other world-lines. The axes of 

 our four-dimensional space-time continuum have been aptly called 

 the to-and-fro axis, the forward-and-backward axis, the up-and-down 

 axis and the sooner-and-later axis, the last, of course, being the time 

 axis. On one side of the origin the time axis represents the past, on 

 the other side the future. Events do not happen, — they are coinci- 

 dences of world-lines, and are simply there, to be met or happened 

 upon, as it were. A few years ago Anderson's new star burst forth. 

 Whatever caused it is supposed to have occurred about the year of 

 George Washington's birth, but we only happened upon a crossing 

 of its world-lines with ours one hundred and seventy years later. If 

 a change is made in an element of our sj'stem, it alters the whole past, 



