5l8 SCIENTIFIC RECREATIONS. 



when farthest from us she is in apogee (the line uniting these points is the 

 line of apsides}, the difference in distance being about 4,000 miles. She 

 passes the sun periodically, and so if the moon moved in the plane of the 

 ecliptic there would be eclipses of the sun and moon twice a month ; but as 

 the orbit is inclined a little, she escapes by moving north or south. We 

 will now endeavour to explain this theory. 



ECLIPSES. 



We have briefly considered the SUN and EARTH and the MOON 

 separately. We are now about to regard the effects produced by them 

 when they come in each other's way and cause ECLIPSES, which are observed 

 with so much interest. There are eclipses of the sun and of the moon. 

 The former occur at the time of new moon, and the latter at full moon ; 

 and this will be at once understood when we remember that the sun is 

 eclipsed by the moon passing between us and the sun ; and the moon is 



eclipsed because the shadow of the earth 

 falls) upon her when she is opposite the 

 sun, and therefore " full." 



Readers of the voyages of Columbus 

 will remember that he managed to obtain 

 supplies from negatively hostile Jamaica 

 savages by pretending to cause an eclipse 

 of the moon, which he knew was about to 

 take place, and to the ancients eclipses were 

 of dire portent. Even in enlightened 

 Rome, to ascribe an eclipse to the causes 

 of nature was a crime. The Chinese have 



Fig. 57i.-soiar eclipse with corona. ' an idea that g reat dragons are devouring 



the moon when she is eclipsed. 



There are total, partial, and annular eclipses. The former terms speak 

 for themselves; the latter name is derived from "annulus," a ring ; for a ring 

 of light is left around the dark portion eclipsed, and is only seen in solar 

 eclipses. In one sense the eclipse of the sun is really an eclipse of the earth, 

 because it is caused by the shadow of the moon falling upon the earth. 



If a bright body, A, be larger than the dark body, B, 

 there will be two kinds of shadows viz., the umbra and the 

 penumbra. For instance, the umbra is the central dark part 

 in the cut (fig. 572), and the penumbra is the lighter portion. 

 As soon as the eye is placed on the umbra, it can perceive 

 no part of the source of light, A, which appears to be eclipsed. 

 On the other hand, the penumbra originates in that locality *'ig. 572- Umbra 



i i /iti ._ ... and penumbra. 



where only a portion of the light proceeding from a luminous 



object can fall ; hence an eye in the penumbra would see a part, but not the 



whole of the illuminating body. This shadow also forms a cone, the apex 



