352 Mr. Blake's Reply to Mr. Qu'mby. 



Mr. Quinby's embarrassment has arisen from not distin- 

 guishing power, in the sense in which the second example re- 

 quires its mensuration, from power in another sense, in which 

 the mensuration of it is not required by the example ; and for 

 the mensuration of which the example does not furnish the 

 data. The three examples were carefully selected, as fur- 

 nishing data for the mensuration of three distinct species of 

 power or of power presenting itself for mensuration, under 

 three different aspects. The first requires the mensuration 

 of power, without relation to time or space. The second re- 

 quires the mensuration of power in its connexion with space, 

 but without relation to time. The third requires the mensu- 

 ration of power, in its connexion with space, and also in its 

 relation to time. The quantity sought by the first example, 

 is a simple determinate quantity ; that sought by the second, 

 is a determinate product of two simple unlike quantities ; and 

 that sought by the third, is indeterminate, being merely a 

 ratio of a product of two simple unlike quantities, to a third 

 quantity, unlike either of them. It is true that a lapse of 

 time will necessarily attend the operation of the power, men- 

 tioned in the second example ; but the operation of a power 

 may be attended not only by this, but by a variety of other 

 circumstances, which may, or may not, become attributes in 

 the mensuration of the power, according to the purpose for 

 which the mensuration is made. It is the purpose for which 

 the mensuration is made, or in other words, the nature of the 

 quantity sought, which determines the number of attributes 

 of which the power to be measured consists. For those cir- 

 cumstances, and those only, attending the operation of a 

 power, which affect the amount of the quantity sought, are to 

 be taken as attributes of the power to be measured. Circum- 

 stances or incidents, which do not affect the amount of the 

 quantity sought, cannot be said to be attributes of the power 

 to be measured, however inseparable their occurrence may 

 be, from the operation of the power. In the mensuration of 

 the power, which produces the result specified in the second 

 example, it is manifest that time cannot affect the amount of 

 the quantity sought ; for it will require the same quantity of 

 power* to produce that result, whether it be effected in a mo- 

 ment, or in a twelve month, or in any longer or shorter period 



* The phrase, quantity of power is here used, as in my former communica- 

 tion, to denote the product of the degree of force and distance. 



