72 Length and Space, 



afterwards corrected, in precisely the same manner. 



12. — It is evident that the idea of length, upon which all 

 these which we are here concerned with depend, cannot be 

 acquired without the assistance of memory. Without this 

 power, the length of no objects can be compared, which 

 do not present themselves to the senses at the same instant 

 of time. Even when two objects are felt by the hand, or 

 seen by the eye, at the same time, it is doubtful whether 

 the mind attends to them both at once. It is more probable, 

 that they are felt and seen successively ; and that the mind 

 attends first to the one and then to the other. Consequently 

 the exercise of memory must be necessary even for the 

 comparison of objects immediately perceived. 



13. — When the mind has been well accustomed to the 

 view of lines, and has actually felt and seen many of them ; 

 it will readily perceive that they are of different kinds. In 

 viewing many different lines, or many different objects 

 that possess length, memory will soon suggest to us, that 

 these lines are not all of the same nature. Thus a rainbow, 

 a coiled rope, and an arrow present appearances extremely 

 different from one another. The impressions which the 

 two latter produce upon the sense of touch are as different 

 as those produced by them upon the sight. A number of 

 trials, while memory compares the present with the past, 

 convinces us, that the impression made by the coil of ropes 

 upon the touch is uniform : and that that upon the sight is 

 also uniform. The impressions made by the arrow upon 

 the same sense are equally uniform. The effects arising 

 from perceiving these two objects by either sense, are per- 

 fectly distinct ; and, thotigh we can never tell in which 

 that difference consists, the difference is so striking, that 

 so long as memory remains, wc are never in any danger 



