DOGMATIC METHODS OF TEACHING. 65 



Newton's theory of gravitation is regarded as the most 

 important and certain theory of physics, and yet 

 gravitation itself is a hypothesis. Then, as to the 

 other branches of physics electricity and magnetism. 

 The whole scheme of these important sciences rests on 

 the hypothesis of " electric fluidity," or of imponderable 

 matter of which the existence is nothing less than 

 proved. Or optics ? Optics certainly appertain to 

 the most important and completest branch of physics, 

 and yet the nndulatory theory of light, which we 

 accept now as the indispensable basis of optics, rests 

 on an unproved hypothesis, on the subjective assump- 

 tion of an ethereal medium, whose existence no one is 

 in a position to prove objectively in any way. Nay, 

 further, before Young set up the undulatory theory of 

 light, for a hundred years the emanation theory as 

 taught by Newton obtained exclusively in physics ; a 

 theory which at the present day is universally regarded 

 as untenable. In our opinion the mighty Newton 

 won the greatest honours in the development of the 

 science of optics, inasmuch as he was the first to 

 connect and explain the vast mass of objective optical 

 facts by a subjective and pregnant hypothesis. But, 

 according to Virchow's view, Newton on the contrary 

 transgressed greatly by teaching this erroneous hypo- 

 thesis ; for even in " exact " physics none but " inde- 

 pendent and certain facts " are to be taught and 



