ANALOGICAL PROOFS. 



the idea that the earth is only an individual of a class of worlds of 

 which the three other planets are members. Look at the 

 annexed plan, fig. 1, which represents the relative positions 

 of these planets in their course round the sun. The position 

 of Mercury is represented at M, that of Venus at V, that of 

 the Earth at E, and that of Mars at M'. The circles represent 

 the paths in which they severally move in going round the 

 sun, which is represented radiating its light and heat from the 

 common centre. 



These four bodies are globular in their form, and not extremely 

 different in their magnitudes. They move round the sun as a 

 common centre in circular orbits, as indicated in the plan, and 

 nearly in the same plane. 



Now the impression is irresistible that these four globes are 



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