GENERALIZATION. 259 



that qualities variable in degree will be found in every 

 substance in a greater or less degree. 



It is highly remarkable that Newton, whose method of 

 investigation was logically perfect, seemed incapable of 

 generalizing arid describing his own procedure. His 

 3elebrated ' Bules of reasoning in Philosophy/ described 

 it the commencement of the third book of the ' Principia/ 

 *re of very questionable truth, and still more questionable 

 value. 



Extreme Instances of Properties. 



Although, as we have seen, substances usually differ 

 ly m degree as regards th'Ir physical properties, great 

 Qterest may attach to particular substances which mani- 

 est a property in a Conspicuous and intense manner. 

 Sveiy branch of physic Science has usually been de- 

 eloped from the attention forcibly drawn to some sin- 

 ular substance. Just as the loadstone disclosed mag- 

 etism and amber frictional electricity, so did Iceland 

 oar point out the existence of double refraction, and 

 Jlphate of quinine the phenomenon of fluorescence. 

 pien one such startling instance has drawn the attention 

 the scientific world, numerous less remarkable cases of 

 ie phenomenon will soon be detected, and it will pro- 

 ibly prove that the property in question is actually 

 nversal to all matter. Nevertheless, the extreme in- 

 arices retain their interest, partly in a historical point of 



jew, partly because they furnish the most convenient 



1 bstances for experiment. 



"Francis Bacon was fully aware of the value of such 

 amples, which he called Ostensive Instances or Light- 

 ing, Free or Predominant Instances. ' They are those ' 

 says, < which show the nature under investigation 

 ked, m an exalted condition/or in the highest degree 



S 2 



