1907-8.] SPACE AND Its DIMENSIONS. 339 
have yet in a way, extension as well as magnitude, and they are always 
projected in some, though often, an indefinite distance. The third dimen- 
sion, if for the time being we may make use of the expression, is thus 
not the product of inference and construction, but it is immediately 
present in every presentation of a surface. Though it may not be the 
object of our attention and measuring apprehension, every space percep- 
tion pre-supposes extension in all directions. 
