ECLIPSES. 



ECLIPSES. 



Or all the occasional astrononomical phenomena, those which have attract- 

 ed most popular attention are LUNAR and SOLAR ECLIPSES. We shall on the 

 present occasion explain the principal circumstances attending l^hem. 



When a luminous body, radiating light in all directions around it, throws 

 these rays upon an opaque body, that body prevents a portion of the rays from 

 penetrating into the space behind it. That portion of the space from which 

 the light is thus excluded by the interposition of the opaque body, is called in 

 astronomy the SHADOW of that body. 



The shape, magnitude, and extent, of the shadow of an opaque body, will 

 depend partly on the shape and magnitude of the opaque body itself, and partly 

 on that of the body from which the light proceeds. 



In the cases before us, the form of the bodies are globes. If the globe of 

 the SUN were equal in magnitude to the globe of the earth, the shadow of the 

 latter would be a cylinder, the base of which would be equal to a great circle 

 of the earth, and such shadow would be interminable, since its sides would be 

 parallel. This will be evident by an inspection of the annexed figure, 1 , in which 

 S. represents the sun, and E. the earth ; the rays <S. E. forming the sides of 

 the shadow, being parallel, could never meet, and consequently the shadow 

 would be infinite, since light can never penetrate into the space between them. 

 If, on the other hand, the sun were a globe less in magnitude than the earth, 

 then the shadow of the latter would have diverging sides as represented in the 

 annexed figure, 2, which would widen as they proceed from the earth, and would 

 be interminable ; but the sun having in reality a diameter about one hundred 

 and twelve times greater than that of the earth,, the rays which proceed 

 from the upper and lower limb of the sun, and which touch the earth at a and b, 

 fig. 3, will converge to certain point at/, behind the earth, and will form a conical 

 space, whose base will be at a b, and whose apex will be at /. From the space 

 enclosed by this cone the light of the sun is entirely excluded, and it is there- 

 fore properly the shadow of the earth. But there is also a certain space be- 

 hind the earth from which the sun's light is only partially excluded, and which 



