120 THE REALITIES OF MODERN SCIENCE 



the volume so that the corresponding numeric would 

 be the same as that expressing the product AH. 



Of course, in this concrete numerical problem we 

 recognize that the unit we should use is the cubic 

 foot, since we are expressing the area in square feet 

 and the height in feet. But we are dealing with an 

 evident problem so that the method which we are em- 

 ploying may not be obscured by incidental difficulties. 

 Let us represent the desired and supposedly unknown 

 unit for volume by (v) ; then, since the numeric corre- 

 sponding to AH is 10X4 we write 



40(0) = 10(1 sq. ft.)X4(lft.) 

 or 0) = (1 sq. ft.)(l ft.)- 



That is, the unit of volume is that of a rectangular 

 parallelepiped for which the base is one unit of area 

 (1 sq. ft.) and the height is one unit of length (1 ft.). 



So far our reasoning has dealt mostly with a concrete 

 numerical example. Concrete numerical illustration, 

 without an expression or development of the general 

 principle involved, was the method of the first textbook 

 of science of which we know, the Ahmes papyrus. 

 This was the work of an Egyptian priest about 1700 

 B.C. and was based upon an earlier text of which no 

 portions have been found, which antedated it by 500 

 years at least. The manuscript describes itself as 

 " Instructions for arriving at the knowledge of all 

 things, and of things obscure, and of all mysteries." 

 If one is satisfied in science with a concrete case and 

 does not go on to abstract the general principle, his 

 attitude will be about that of the ancient Egyptian. 

 It was the Greeks, as we saw, who started science 



