380 



A CENTURY OF SCIENCE 



electric and magnetic intensities. These modes of repre- 

 sentation have been and still are of the greatest use and 

 importance, but their value in scientific description must 

 not lead to lack of appreciation of their purely specula- 

 tive character. 



Finally attention must be drawn to the fact that the 

 discoveries of inductive science, embodied in the great 

 generalization we have just been discussing, have led to 

 a more intimate knowledge of the nature of time and 

 space than twenty centuries of introspection on the part 

 of professional philosophers. Minskowski, whose prom- 

 ise of greater achievement was cut off by an untimely 

 death, has shown that four dimensional geometry makes 

 possible the representation with beautiful simplicity of 

 the time and space relationships of this theory. The 

 one time and three space dimensions merge in such a 

 manner as to form a single whole with not a vestige of 

 differentiation between these fundamental quantities. 

 Wilson and Lewis 15 have made this representation famil- 

 iar to American readers through their admirable trans- 

 lation of Minskowski 's work into the notation of Gibbs's 

 vector analysis. 



Aberration, the Doppler effect, anomalous dispersion, 

 indeed all known phenomena, are found to be in 

 accord with the principle of relativity. It must be 

 borne in mind, however, that this principle applies only 

 to systems moving relative to one another in straight 

 lines with constant velocities. That there is something 

 absolute about rotation has been recognized since Fou- 

 cault performed his famous pendulum experiment in 1851. 

 This experiment (C. S. Lyman, 12, 251 and 398, 1851) 

 consisted in setting a pendulum composed of a heavy 

 brass ball suspended by a long wire into oscillation in 

 such a way as to avoid appreciable ellipticity in its 

 motion. Observation of the rate at which the ground 

 rotates relative to the plane of vibration of the pendulum 

 furnished a method of measuring the rotation of the 

 earth about its axis without reference to celestial bodies. 

 The gyroscopic compass in use to-day provides yet 

 another terrestrial method of detecting this rotation. 



The Future of Physics. At times during the history 

 of physics it has seemed as if the fundamental laws of 



