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nature, that scarcely any one could have formed a conjecture 

 about them previously to their discovery, bat would rather 

 have ridiculed them as impossible. For men are wont to 

 guess about new subjects from those they are already ac 

 quainted with, and the hasty and vitiated fancies they have 

 thence formed: than which there cannot be a more fallacious 

 mode of reasoning, because much of that which is derived 

 from the sources of things does not flow in their usual 

 channel. 



If, for instance, before the discovery of cannon, one had 

 described its effects in the following manner: There is a new 

 invention by which walls and the greatest bulwarks can be 

 shaken and overthrown from a considerable distance; men 

 would have begun to contrive various means of multiplying 

 the force of projectiles and machines by means of weights 

 and wheels, and other modes of battering and projecting. 

 But it is improbable that any imagination or fancy would 

 have hit upon a fiery blast, expanding and developing itself 

 so suddenly and violently, because none would have seen an 

 instance at all resembling it, except perhaps in earthquakes 

 or thunder, which they would have immediately rejected as 

 the great operations of nature, not to be imitated by man. 



So, if before the discovery of silk thread, any one had 

 observed, That a species of thread had been discovered, fit 

 for dresses and furniture, far surpassing the thread of 

 worsted or flax in fineness, and at the same time in tenac 

 ity, beauty, and softness; men would have begun to im 

 agine something about Chinese plants, or the fine hair of 

 some animals, or the feathers or down of birds, but certainly 

 would never have had an idea of its being spun by a small 

 worm, in so copious a manner, and renewed annually. But 

 if any one had ventured to suggest the silkworm, he would 



