'i()0 Professor Whewell on the Mathematical Exposition 



of the vehemence of desire, and the urgency of need which men 

 have, as well as of their extent of means. A member of this 

 University who formerly applied mathematical reasoning to some 

 <|\iestions of this kind, proposed to measure demand by con- 

 sidering the latter element (the means of purchasing) as constant, 

 the desire and the difficulty balancing each other so as to pre- 

 serve this constancy. 



He supposed (merely as a means of reducing questions to 

 calculation) that men set aside a certain sum to purchase a given 

 article, and that this sum 'neasures the demand. If the article 

 increase in price they buy just so much less, if it become cheaper 

 they purchase so much more. The price therefore will vary 

 inversely as the supply, (not speaking with popular laxity, 

 but in mathematical strictness.) Now this mode of beginning 

 the reasoning, answers extremely well the purpose of avoiding 

 all indefiniteness, and offers a kind of approximation to the 

 law which really obtains as to changes of prices; but probably 

 the approximation is a very loose and inaccurate one. Accord- 

 ing to this estimate, the failure of \ the crop of corn, for instance, 

 would increase the price by \. It is nearly certain that the 

 increase would be much greater. A statement has been made 

 by some writers which we may use as affording a nearer ap- 

 proximation than the one just mentioned, and as shewing the 

 nature of the dependence of the quantities concerned, without 

 resting any thing upon its exactness. According to the writers 

 now referred to, we have the following progression*: 



A defect in the harvest of ^ raises the price of corn ^ 



* Sec Tooke, on Higli and Low Prices, p. 2S5. 



