: 22 THE POPULAR SCIENCE MONTHLY. 



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selves ! ' ' Copernicus,' I replied, ' could not understand it better 

 This novel theme continues to occupy them during their return to the 

 house, and the first evening secures her belief for the new system. 



The next morning, on Fontenelle's sending to ask how the lady 

 has passed the night, and to politely inquire whether she has been 

 able to sleep while turning, he is assured that she has already got 

 used to the motion, and was able to rest as soundly as Copernicus 

 himself could have done. With so apt a scholar, progress is rapid, 

 and, by evening, we find them discussing the habitability of the 

 moon, and the cause of the sun's light and heat. What is the view 

 of our author (the subsequent secretary of the Academie des Sciences, 

 and an authority in his day) on the source of supply for this immense 

 expenditure of the solar energy V What theory does he adopt how 

 was it accounted for in his time ? Listen to the explanation of the 

 man who has just satirized so happily the fallacies of the schoolmen. 

 It shines because " it is self-luminous in its nature." And this is 

 given in good faith by Fontenelle as a reason ! 



Clever as he is, he is here in the bondage of his age ; but he might 

 yet have taken a lesson from a contemporary, who, though pretending 

 to no * philosophy," had seen and laughed at the weakness of the 

 learned of his time in thus making words do duty for facts. We 

 remember how the candidate for medical honors in the " Malade Ima- 

 ginaire," on being asked why opium induces sleep, replies to the de- 

 lighted satisfaction of the examining Faculty that it is because it 

 possesses a soporific quality ! W'hen we see a man so acute as Fonte- 

 nelle giving a precisely similar answer, with an obtuseness so plain 

 to us, so imperceptible to him, can anything suggest more pertinently 

 the need of watchfulness for traces of this legacy of ancient fallacies 

 of thinking in our own modes of thought ? 



The third evening is occupied with a further discussion of the 

 moon, and of Venus ; on the fourth the other planets are considered, 

 and reasons given for their possible habitability, some of which would 

 hardly satisfy a more modern philosopher. Thus, the ingenious but 

 scarcely satisfactory suggestion is made that, in spite of the neigh- 

 borhood of Mercury to the sun, that planet may be a comfortable 

 residence, owing to the presence there of large quantities of saltpetre, 

 a substance which (according to our author) gives out "cold exhala- 

 tions " in the sunshine. Lest this idea be unacceptable to our skeptical 

 age, it should be added that Fontenelle takes care to fortify his posi- 

 tion by citing the case of China, large portions of which, it appears, 

 in spite of a southern latitude, experience extreme cold, even to the 

 freezing up of their rivers in July, on account of the existence of this 

 ingredient in their soil ! 



The " vortices" of Descartes are here introduced and offered as an 

 explanation of the motions of the Jovian satellites about their pri- 

 maries, and of the principal planets about the sun ; and, in the next 



