SUMMARY. 287 



quantity must be adopted ; before a comparison can 

 be made between two quantities, it is necessary to 

 determine a unit of measure common to the two. 



The " kind " of a function may, in some cases, be 

 stated in terms of time and quantity. 



The properties of inorganic things vary less than 

 those of living subjects. 



The consideration of the attributes of properties 

 in two or more subjects raises some important pro- 

 blems. The time of growth, or movement, in three 

 subjects, A, B, C, may occur separately in each or 

 may coincide in any of the combinations A, B, C, 

 AB, AC, BC, ABC : thus considerations of time lead 

 to coincidences, combinations, sequences, series. 



As to quantities of growth, or movement, in two 

 or more subjects, we are now able to make ratios or 

 proportions. Proportional growth, inasmuch as it 

 concerns a proportion, must imply something about 

 the quantity of the growth ; it is only as to quan- 

 tities that we can make a proportion, or ratio. The 

 term proportional growth is applicable to two 

 subjects : it concerns the ratio of growth ; and 

 denotes the proportion of the quantity of the 

 growth in the one subject, to the quantity of 

 growth in the other subject. 



The term equal proportional growth implies that 

 two ratios are equal. Two subjects, each present- 

 ing two similar parts for comparison, are referred 

 to ; the ratio of the quantity of growth in the two 

 parts of the one subject, is said to be equal to the 

 ratio of the quantity of -growth in the two cor- 

 responding parts of the other subject. 



