xxx.] CLASSIFICATION. 67ft 



Perhaps it will be found in the sequel, that classification 

 is not only the beginning, but the culmination and the end, 

 of human knowledge." 



Classification Involving Induction. 



The purpose of classification is the detection of the laws 

 of nature. However much the process may in some cases 

 be disguised, classification is not really distinct from the 

 process of perfect induction, whereby we endeavour to 

 ascertain the connexions existing between properties of the 

 objects under treatment. There can be no use in placing 

 an object in a class unless something more than the fact 

 of being in the class is implied. If we. arbitrarily formed 

 a class of metals and placed therein a selection from the 

 list of known metals made by ballot, we should have no 

 reason to expect that the metals in question would resemble 

 each other in any points except that they are metals, and 

 have been selected by the ballot. But when chemists 

 select from the list the five metals, potassium, sodium, 

 caesium, rubidium, and lithium and call them the Alkaline 

 metals, a great deal is implied in this classification. On 

 comparing the qualities of these substances they are all 

 found to combine very energetically with oxygen, to decom- 

 pose water at all temperatures, and to form strongly basic 

 oxides, which are highly soluble in water, yielding power- 

 fully caustic and alkaline hydrates from which water cannot 

 be expelled by heat. Their carbonates are also soluble in 

 water, and each metal forms only one chloride. It may also 

 be expected that each salt of one of the metals will correspond 

 to a salt of each other metal, there being a general analogy 

 between the compounds of these metals and their properties. 



Now in forming this class of alkaline metals, we have 

 done more than merely select a convenient order of 

 statement. We have arrived at a discovery of certain 

 empirical laws of nature, the probability being very con- 

 siderable that a metal which exhibits some of the properties 

 of alkaline metals will also possess the others. If we 

 discovered another metal whose carbonate was soluble in 

 water, and which energetically combined with water at all 

 temperatures, producing a strongly basic oxide, we should 

 infer that it would form only a single chloride, and that 



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