The History of Things 81 



"a mode of motion.** Some which are not re- 

 ducible at present will probably undergo simpli- 

 fying analysis in the future, for the physicist may 

 some day discover the true inwardness of gravita- 

 tion, and be able to tell us what really happens in 

 the invisible world when the apple falls in the 

 orchard. Progress is continuous toward the ideal 

 of redescribing all the occurrences in inanimate 

 nature in terms of the laws of motion; one fastness 

 after another has given up its keys; one riddle 

 after another has been read ; all of which means a 

 scientific demonstration of the unity of nature. 



It is true that the redescriptions which are given 

 of intricate occurrences do not sound simple; the 

 more thorough they are, the more do they pass be- 

 yond the comprehension of the unlearned and 

 become preserves for the mathematically minded; 

 even more than in ancient days is it true that the 

 portal of the scientific academy bears the legend, 

 "Let no one ignorant of mathematics enter here." 

 But the point is that the assumptions of the me- 

 chanical interpretation of inanimate nature are 

 simple, in the sense that the laws of motion are 

 simple. It comes to this, then, that the birth and 

 death of worlds, the harmony of the spheres, the 

 sweep of our whole solar system in space — in short, 

 the greatest of cosmic phenomena — submit to 

 being studied by the same exact methods, and to 

 being redescribed in the same simple terms as the 



