BINARY STAKS. 



greater, let the larger sun with its planets be represented at s, 

 fig. 7, in the focus of an ellipse, in which the lesser sun accompanied 

 by its planets moves. At A 

 this latter sun is in its peri- 

 helion, and nearest to the 

 greater sun s. Moving in 

 its periodical course to B, it 

 is at its mean distance from 

 the sun s. At D it is at 

 aphelion, or its most distant 

 point, and finally returns 

 through c to its perihelion 

 A. The sun s, because of 

 its vast distance from the 

 system A, would appear to th e 

 inhabitants of the planets of 

 the system A much smaller 

 than their proper sun ; but, 

 on the other hand, this effect 

 of distance would be to a 

 certain extent compensated 

 by its greatly superior mag- 

 nitude ; for analogy justifies 

 the inference that the sun s 

 is greater than the sun A in 

 a proportion equal to that of 

 the magnitude of our sun 

 to one of the planets. The 

 inhabitants of the planets of 

 the system A will then behold 

 the spectacle of two suns in their firmament. The annual motion 

 of one of these suns will be determined by the motion of the 

 planet itself in its orbit, but that of the other and more distant 

 sun will be determined by the period of the lesser sun around the 

 greater in the orbit A B D c. The rotation of the planets on their 

 axes will produce two days of equal length, but not commencing 

 or ending simultaneously. There will be in general two sunrises 

 and two sunsets ! When a planet is situate in the part of its 

 orbit between the two suns, there will be no night. The two suns 

 will then be placed exactly as our sun and moon are placed when 

 the moon is full. When the one sun sets, the other will rise ; and 

 when the one rises the other will set. There will be, therefore, 

 continual day. On the other hand, when a planet is at such a 

 part of its orbit that both suns lie in nearly the same direction as 

 seen from it, both suns will rise and both will set together. There 



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