84 HISTORY OF ASTRONOMY. 



This fact will appear the more striking if we draw a 

 diagram representing the orbits of all the known planets 

 in their proper proportions. We shall find that while 

 the orbits of Mercury, Venus, the Earth, and Mars are 

 quite detached from each other, and the orbits of Jupiter, 

 Saturn, Uranus, and Neptune are separated by intervals 

 which the imagination can with difficulty grasp, between 

 Mars and Jupiter is a cluster of bodies whose orbits are so 

 interlaced as to suggest the apprehension of frequent and 

 inevitable collision. 



The diagram on the following page represents the or- 

 bits of nine of these small planetary bodies, designed to 

 be selected so as to afford a tolerable specimen of the 

 whole. The other thirty-one orbits are omitted, to avoid 

 the confusion of so many lines in a single diagram. In 

 one respect this representation is calculated to convey an 

 erroneous impression. All the orbits are represented as 

 situated in the same plane, whereas, in reality, no two of 

 them are situated in the same plane. These planes all 

 pass through the sun, and are inclined to the earth's orbit 

 in angles indicated in column sixth of the preceding 

 Table. One half of each orbit must therefore be below 

 the earth's orbit, and the other half above it ; and in order 

 to indicate as fully as possible the actual position of these 

 orbits, the portion which falls below the plane of the 

 earth's orbit is indicated by a dotted line, while the re- 

 mainder is indicated by a continuous black line. These 

 orbits, then, do not really intersect each other as repre- 

 sented in the diagram. Indeed, no two of the planetary 



