108 THE BEASON WHY. 



" And God said, Let there be light : and there was light. 



one be discouraged by the fact that the theory of light, as, indeed, of all the 

 imponderable agents, is imperfectly understood. Rather Jet us rejoice that 

 there are vast fields of discovery yet to be explored ; and that light, the most 

 glorious and inspiring element in nature, invites us from the sun, the moon, 

 and the stars, and from the face of every green leaf and variegated flowet, 

 to search out the wonders of its nature, and further to exemplify the goodness 

 and .wisdom of God. 



452. What is the distance of the sun from the earth? 

 Ninety five millions of miles. 



453. At ivhat rate of velocity does light travel f 



At the rate of 192,000 miles in a second, through our atmo- 

 sphere ; and 192,500 miles in a second through a vacuum. 



454. Sow long does light take to travel from the sun to 

 the earth ? 



Eight minutes and thirteen seconds. 



455. What is the constitution of the sun ? 



It is a spherical body, 1,384,472 times larger than the earth. 



456. From what does the luminosity of the sun arise f 

 From a luminous atmosphere, or, as M. Arago named it, photo- 

 sphere, which completely surrounds the body of the sun, and which 

 is probably burning with great intensity. 



457. What are the minor sources of light? 



Light may be produced by chemical action, by electricity, and 

 by phosphor esence, in the latter of which various agencies unite. 



458. What is a ray of light ? 



A ray of light is the smallest portion of light which we can 

 recognise. 



459. What is a medium ? 



A medium is a body which affords a passage for the rays o 

 Might. 



460. What is a learn of light ? 



A beam of light is a group of parallel ravt. 



461. What is a pencil of light? 



