104 Irving Fisher — Mathematical investigations 



again a physical analogue. Water seeks its level, but this law does 

 not fully explain Xiagara. A great deal of special data are here 

 necessary and the physicist is as unfit to advise the captain of the 

 Maid of the Mist as an economist to direct a Wall street speculator. 

 The failure to sej^arate statics from dynamics appears historically* 

 to explain the great confusion in early physical ideas. To make 

 this separation required the reluctant transition from the actual 

 world to the ideal. The actual world both physical and economic 

 has no equilibrium. " Xormal"f price, production and consumption 

 are sufficiently intricate without the complication of changes in social 

 structure. Some economists object to the notion of "normal " as an 

 ideal but unattainable state They might with equal reason object 

 to the ideal and unattainable equilibrium of the sea. 



The dynamical side of economics has never yet received system- 

 atic treatment. When it has, it will reconcile much of the present 

 apparent contradiction, e. g. if a market is out of equilibrium, things 

 may sell for " more than they are worth," as everj^ practical man 

 knows, that is the proper ratios of marginal utilities and prices are 

 not preserved. 



We have assumed a constant population. But population does 

 chano^e and with it all utilitv functions change. An analvsis whose 

 independent variable is population]; leads to another department of 

 economics. In the foregoing investigation the influence of popula- 

 tion was included in the form of the utility function. So also with 

 all causes physical, mental and social not dependent on the quantities 

 of commodities or services. 



Individuals are not free to stop consuming or producing at any 

 point. Factory operatives must have uniform working hours. The 

 marginal undesirability of the last hour may for some workmen 

 equal, for others exceed or fall short of the utility of its wages. 



§8. 



No one is fully acquainted with all prices nor can he adjust his 

 actions to them with the nicety supposed ; both these considerations 

 are starting points for separate discussion. 



*Wliewell, Hist. Induct. Sci., I, 72-3 and 186. -f MarshaU, p. 84. 



X See article of Prof. J. B. Clark. Distribution as determined by a law of 

 rent. Qiiart. Jour. Econ., Apr. '91, p. 289. 



