IRREGULAR REFLECTION. 



reflects a certain quantity of rays. That they do so we perceive 

 by the fact that they are visible. The eye recognises such surfaces 

 as differing from a dark aperture not occupied by any material 

 surface, and it can only thus recognise the appearance of the ma- 

 terial surface by the light which it reflects. The following expe- 

 riment, however, will render this more evident. 



11. Blacken the inside of a tube, and fasten upon the extremity 

 remote from the eye a plate of glass. To the centre of this plate 

 of glass attach a circular opaque disk, somewhat 



less in diameter than the tube, so that in looking 

 through the tube a transparent ring will be 

 visible, as represented in fig. 4. In the centre 

 of this transparent ring will appear an intensely 

 dark circular space, being that occupied by the 

 disk attached to the glass. 



Now, let a piece of black velvet be held oppo- 

 site the end of the tube, so as to be visible through the transpa- 

 rent ring. If the velvet reflected no light, then the transparent 

 ring would become as dark as the disk in the centre ; but that 

 will not be the case. The velvet will appear by contrast with the 

 disk, not black, but of a greyish colour, proving that a certain 

 portion of light is reflected, which in this case is rendered percep- 

 tible by the removal of the brighter objects from the eye. 



12. Irregular reflection, as it has been so improperly called, is 

 one of the properties of light which is most essential to the effi- 

 ciency of vision. 



"Without irregular reflection, light must be either absorbed by 

 the surfaces on which it falls, or it must be regularly reflected. 

 If the light which proceeds from luminous objects, natural or arti- 

 ficial, were absorbed by the surface of objects not luminous, then 

 the only visible objects in the universe would be the sun, the stars, 

 and artificial lights, such as flames. 



These luminaries would, however, render nothing visible but 

 themselves. 



If the light radiating from luminous objects were only reflected 

 regularly from the surface of non-luminous objects, these latter 

 would still be invisible. They would have the effect of so many 

 mirrors, in which the images of the luminous objects only could be 

 seen. Thus, in the day-time, the image of the sun would be 

 reflected from the surface of all objects around us, as if they were 

 composed of looking-glass, but the objects themselves would be 

 invisible. The moon would be as though it were a spherical 

 mirror, in which the image of the sun only would be seen. A 

 room in which artificial lights were placed would reflect these 

 lights from the walls and other objects around as if they were 



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