150 TKEMIXQLOGY. . 139. 



binations may be considered as the elements of the know- 

 ledge of multiple combinations ; and a triple combination 

 may be resolved into two, a quadruple combination into 



six, one consisting of n simple forms, into n . .~Z ' 

 binary combinations. 



. 139. FIRST LAW OF COMBINATION. 



The first Law of Combination is : That the 



combined simple Jbrms must belong not only to the 



same System (. 135.), but also to the same Series of 



Crystallisation (. 136.);'*Aiy must be derived 



from one and the same Fundamental Form. 



If one of the simple forms contained in a combination, 

 belong to a certain System of Crystallisation, the rest of 

 them also must belong to the same system. Let, for in- 

 stance, this form be a regular six-sided prism ; the rest of 

 the forms combined with it will belong to the rhombohe- 

 dral system ; and thus one single form recognised in a 

 combination, though it be a limiting one, will be sufficient 

 to determine the System of Crystallisation (. 137-). But 

 the form recognised may be a finite one, and moreover it 

 may be, according to its dimensions, a member of the Se- 

 ries of Crystallisation peculiar to rhombohedral Lime-ha- 

 loide ; the rest of the forms will belong to the same series 

 (though from this only it does not necessarily follow that 

 the individual is rhombohedral Lime-haloide) ; and their 

 dimensions may be calculated, as soon as we know in what 

 relation they stand to that which has been determined. 

 Hence also, in this case, the observation of one single form 

 suffices for determining the whole Series of Crystallisation 

 to which all the simple forms of the combination belong 

 (. 137.). Nature confirms this law in all combinations, 

 without any exception. 



The only combinations to be considered in Crystallogra- 



