xxiii.] THE USE OF HYPOTHESIS. 513 



is derived from sensation we cannot figure to ourselves 

 any agent, but as endowed with some of the properties of 

 matter. A.11 that the mind can do in the creation of new 

 existences is to alter combinations, or the intensity of 

 sensuous properties. The phenomenon of motion is 

 familiar to sight and touch, and different degrees of rapidity 

 are also familiar ; we can pass beyond the limits of sense, 

 and imagine the existence of rapid motion, such as our 

 senses could not observe. We know what is elasticity, 

 and we can therefore in a way figure to ourselves elasticity 

 a thousand or a million times greater than any which is 

 sensuously known to us. The waves of the ocean are many 

 times higher than our own bodies ; other waves, are many 

 times less ; continue the proportion, and we ultimately 

 arrive at waves as small as those of light. Thus it is that 

 the powers of mind enable us from a sensuous basis to 

 reason concerning agents and phenomena different in an 

 unlimited degree. If no hypothesis then can be absolutely 

 opposed to sense, accordance with experience must always 

 be a question of degree. 



In order that an hypothesis may allow of satisfactory 

 comparison with experience, it must possess definiteness 

 and in many cases mathematical exactness allowing of 

 the precise calculation of results. We must be able to 

 ascertain whether it does or does not agree with facts. 

 The theory of vortices is an instance to the contrary, for 

 it did not present any mode of calculating the exact 

 relations between the distances and periods of the planets 

 and satellites ; it could not, therefore, undergo that rigorous 

 testing to which Newton scrupulously submitted his theory 

 of gravity before its promulgation. Vagueness and in- 

 capability of precise proof or disproof often enable a false 

 theory to live; but with those who love truth, vagueness 

 should excite suspicion. The upholders of the ancient 

 doctrine of Nature's abhorrence of a vacuum, had been 

 unable to anticipate the important fact that water would 

 not rise more than 33 feet in a common suction pump. 

 Nor when the fact was pointed out could they explain it, 

 except by introducing a special alteration of the theory to 

 the effect that Nature's abhorrence of a vacuum was 

 limited to 33 feet. 



L L 



