Principles of Political Economy and Taxation. 167 



and in difficult problems of physics, it is precisely by such a 

 simplification as this, that a first approximation is obtained. 

 Thus in the investigation of the problem of the tides, we have 

 a very complex case of the motion of a fluid : but Newton's 

 mode of treating the question was, to consider what would be 

 the form of equilibrium of the ocean, acted upon by the forces 

 which produce the tides: and this solution of the problem, though 

 necessarily inexact, was accepted as the best which could easily 

 be obtained. The investigations of Laplace and others who have 

 since treated the problem on its true grounds, as a question of 

 hydrodynamics, have shewn that Newton's solution explains rightly 

 the main features of the phenomenon. 



In order however that solutions of this nature may have any 

 value, it is requisite that the principles, of which we estimate 

 the operation, should include all the predominant causes which 

 really influence the result. We necessarily reject some of the 

 circumstances and tendencies which really exist: but we can do 

 this with propriety, only when the effects of these latter agents 

 are, from their small amount or short duration, inconsiderable 

 modifications only of the general results. The quantities which 

 we neglect must be of an inferior order to those which we take 

 into account ; otherwise we obtain no approximation at all. We 

 may with some utility make the theory of the tides a question 

 of equilibrium, but our labour would be utterly misspent if 

 we should attempt to consider on such principles the theory of 

 waves. 



It appears to be by no means clear that the irregular fluctu- 

 ations and transitory currents by which the elements of wealth 

 seek their natural level may be neglected in the investigation of 

 the primary laws of their distribution. It is not difficult to con- 



