ANCIENT AXIOMS AEE NOT UNCHANGEABLE. 19 



principles of the sciences. There was a time when many 

 of these truths were not known, but as science advances 

 we become acquainted with a greater number of its 

 axioms and laws, and uniformity of belief on fundamental 

 points enlarges also. Neither our knowledge nor our 

 accuracy in science is intuitive ; they both are results of 

 experience and education. In consequence of limited 

 knowledge and instruction, the human mind can think 

 erroneously, and often does so, but the tendency to think 

 falsely in natural subjects diminishes as education ad- 

 vances. Erroneous propositions which were formerly 

 believed, become absurd and almost unthinkable by the 

 progress of science. There was a time when men thought 

 that the earth was a plane, that the sun and planets 

 revolved round it ; that matter was destroyed by burning, 

 &c. ; but such propositions have become comparatively 

 inconceivable by nearly all intelligent minds. The ancient 

 axiom that the circle was the most perfect of figures, that 

 natural motion must be circular, and therefore that the 

 planets must move in circular orbits, was believed until 

 the time of Kepler, but is now no longer an axiom. That 

 which is inconceivable by one man, or in one age, is not 

 necessarily so by another man, or in another period, and 

 therefore the inconceivability of an idea or the reverse is 

 only an incomplete test of its truth. Ideas which at 

 one period are beyond reason, do in many cases, by the 

 progress of knowledge, come within its domain ; and some 

 of those which were thought to be true are proved to be 

 false. Some discoveries which are unattainable in one 

 age or state of knowledge become attainable in another ; 

 for instance, the laws of electro-magnetism or of electro- 

 chemical action could not have been discovered in an age 

 when electro-currents were unknown, nor could the prin- 

 ciple of conservation of matter and of energy have been 



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