AN APOLOGY FOR THE CHURCH S PERSECUTION OF SCIENCE 171 



Take, for example, the principle of the irrigating ditch. That 

 principle was discovered when men's thoughts were still animistic. 

 The first irrigator of Babylonia must have expressed the principle in 

 some such terms as this: "Father Euphrates is marching toward the 

 sea; if we induce or compell him to pass through our fields he will 

 bless them." After long ages animism passed away. Men learned 

 to think of matter as inanimate. The primitive conception of the 

 principle of irrigation therefore of necessity likewise passed. It shared 

 the death of the body of ideas of which it formed a part. But the 

 principle itself survived. It rose again embodied in a new idea ; the 

 idea that water always runs down hill. That idea was eventually seen 

 to be a particular case of a more general principle, that most things if 

 unsupported fall to the earth. Then Newton taught the world that 

 the force of gravity is exerted, not by the earth alone, but by every 

 particle of matter, and set forth the laws which govern its working. 

 At present we seem to be on the verge of a new conception of gravita- 

 tion. The new conception of matter which physical chemistry has 

 recently evolved demands one. 



Thus the principle of the irrigation ditch, when its history is 

 studied, resolves itself into at least four successive conceptions; with 

 a fifth conception just below the horizon. The bond which unites 

 these conceptions is an identity of usefulness. All enforce upon the 

 irrigator identical injunctions. All embody the same working hy- 

 pothesis. The useful working directions which the irrigators of ancient 

 Babylonia derived from their idea of the habits of Father Euphrates 

 are equally derivable from Newton's theory of gravitation. They will 

 be equally derivable from the new conception of gravitation which 

 scientists are laboring to evolve. The language in which the ancient 

 Babylonian farmer expressed his working hypotheses, the conceptions 

 in which he pictured it to himself, were inadequate. Our description 

 of the truth upon which all successful irrigation rests is but Uttle less 

 inadequate. Only omniscience, as we have seen, can adequately con- 

 ceive any reality. But every builder of a successful irrigating ditch, 

 as he builds, is acting in harmony with reality; as is proved by his 

 success. A valid rule of art, once discovered, abides as a permanent 



