DISCOVERY BY MEANS OF INFERENCE. 595 



theory of terrestrial magnetism, and published it in the 

 year 1839. According to this theory, the earth has only 

 two magnetic poles, or places where a freely suspended 

 magnetic needle places itself in a vertical position. 



Important scientific discoveries have in various in- 

 stances been long overlooked in consequence of our finite 

 powers of inference. Ofeber, an Arabian alchemist, who 

 was born in 830, discovered and published the fact that, 

 by heating iron, lead, or copper to redness and cooling it, 

 its weight was increased ; Boyle also, during the seven- 

 teenth century, obtained a similar result with tin ; but 

 nevertheless, in the face of these facts and of greatly 

 increased chemical knowledge, 850 years afterwards (i.e. 

 1720), they remained misunderstood, and Beccher and 

 Stahl published, and chemists in general accepted, the 

 erroneous theory of phlogiston, which from Berlin spread 

 all over Europe. Every human invention and theory, 

 however improved, is only an advance on its predecessors, 

 and is more or less imperfect ; this one was a great im- 

 provement upon previous ones, because it grouped together 

 a great many chemical ideas into an apparently har- 

 monious system, and the wonder is, not that it was defec- 

 tive, but that so great a step was made in advance as to 

 develop it at all ; imperfect as it was, it enabled chemists 

 to express more simply and clearly many important and 

 extensive truths. The theory of Beccher, developed by 

 Stahl, and published by him between the years 1700 and 

 1730, was an inference from the appearance of nearly all 

 previously-known chemical facts of oxidation, combustion, 

 and reduction of metals, &c. ; it was, however, an erroneous 

 inference, which looked like a true one because it appeared 

 consistent in nearly all its parts. 



The modern theory of chemistry, founded largely by 

 Lavoisier in 1778, was also evolved by means of inferences 



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