THE SEASON WHY. 110 



" The day is thine, the night also is thine : thou hast prepared the light and 

 the sun." PSALM LXXIV. 



Because the rays of light from our faces are reflected by the 

 surface of the quicksilver at the back of the glass. 



513. Why does the quicksilver reflect the rays of light ? 



Because, being densely opaque to light, and presenting also a 

 bright surface, it is a good reflector, and it throws back the whole 

 of the rays. 



514. What has the glass to do with the rejection ? 



The glass has nothing to do with the reflection, except that it 

 affords a field upon which the reflecting surface of the quicksilver is 

 spread ; and it keeps the air and dirt from dulling the quicksilver. 



The parts of a mirror from which the quicksilver is rubbed away give no 

 reflection that could assist the reflecting power of the quicksilver. That the 

 surface of the glass does not reflect the image, is shown by the fact, that if you 

 put the point of any object against the glass, the thickness between the point 

 and the place where the reflection of it begins, will show the exact thickness of 

 the glass. 



515. Why does a compound mirror (a multiplying mirror) 

 exhibit a large number of images of one object. 



Because all objects reflect rays of light in every direction, and 

 therefore the different mirrors, being at various angles, receive each 

 a reflection of the same object. 



516. Why does a window-pane appear to be a better reflec- 

 tor- by candle-light than by day -light ? 



The reflecting power of glass is precisely the same by night as by 

 day, and is always very feeble. But it appears to be greater by 

 night, because the surrounding darkness increases the apparent 

 strength of the reflection. 



517. How do we know that objects reflect light in every 

 direction? 



Because if we prick a hole in a card with a pin, and then look 

 through that small hole upon a landscape, we can see some miles 

 of country, and some thousands of objects ; every part of every 

 object throughout the whole scene, must have sent rays of light to 

 the small hole pricked in the card. 



