X PREFACE. 



be said to be a medium for teaching the properties 

 of natural objects, the definition is equally unhappy 

 as if it were said that the system of the universe 

 enables mankind to acquire a knowledge of itself, 

 that is, of the various properties of the heavenly 

 bodies. In natural philosophy a system has usually 

 indeed been considered as synonymous with an 

 hypothesis ; but the two ideas expressed by these 

 words have of late been very properly distinguished 

 by observing that though a mere fiction or hypo- 

 thesis may explain phenomena, yet a system is a 

 certainty that must be deduced from these. The 

 existence of particular phenomena can therefore 

 never be legitimately proved or explained by a sy- 

 stem, though they are virtually included in it, much 

 in the same manner as in the statement of a pro- 

 position all those facts are assumed upon which its 

 demonstration may depend. 



When it is considered that in proportion to the 

 number of data used in any investigation, the greater 

 is the accuracy of the result, there seems little dif- 

 ficulty in allowing that the perfect knowledge of the 

 natural system must consist in that of all the phe- 

 nomena of natural history. This is moreover in 

 no small degree rendered probable, though not ab- 

 solutely confirmed, by the well known circumstance 

 that the observations, whether of distinction or affi- 

 nity, which are taken from the consideration of any 



