22 PROPERTIES OF LENSES. 



does not act dioptrically under certain circumstances, 

 and that we have a new aid to research in these dif- 

 fraction phenomena; like polarisation and other pro- 

 perties of light. 



Unfortunately the whole stress has been laid upon 

 the fact that these images are not exact representa- 

 tions of material forms. 



Association and inherited materialism has taken 

 too great a hold upon our minds, and we have for- 

 gotten that the same thing was proved with regard 

 to all images many years ago ; namely that nothing 

 more can safely be inferred from the image presented 

 to the eye, than the presence in the object of such 

 structural peculiarities, as will produce the particular 

 refraction phenomena on which the image depends. 



Almost all scientists are misled by the error of 

 conceiving material things to exist apart from the 

 mind that perceives them, we do not mean by this 

 that their esse is a mere perci'pi. 



Some of our foreign brethren have justly said, 

 " the English are that nation in Europe which like 

 the Huckster and Workman Class of the state are 

 destined to pass their lives immersed in matter." 

 We raise a shout of astonishment at an old idea, no 

 doubt in a new dress, and we miss the great dis- 

 covery itself in our delight of at last perceiving by 

 it, what has been dimly present to our minds for 

 centuries. 



These diffraction phenomena must not be con- 

 founded with those appearances surrounding the 

 outlines of an object, mentioned in a previous para- 

 graph when speaking of correction for cover glass. 



