i<)oj\ Henderson — Foundations of Geometry. 23 
would doubtless be: “Although it can never be mathematically 
demonstrated, our space I believe to be Euclidian space be- 
cause of the testimony of experience.” The three angles of 
a triangle can never be mathematically demonstrated to be 
equal to two right angles; nor can experience ever give the 
absolutely exact metric results desiderated. And yet, this 
thing amounts to what we crudely call “moral certainty”, 
viz. that the “practical geometry”, as Bessel rightly called 
it, within reasonable limits of error — for which we must 
always allow in this imperfect world — , and for limited por- 
tions of space, is Euclidian. So, after all, it seems that 
we are forced to the conclusion that the axioms of geom- 
etry, although they are, abstractly speaking, assump- 
tions, are, practically speaking, deductions from expe- 
rience. Only as suppliants at the feet of Nature her- 
self can we ever hope to penetrate to the heart of her mys- 
tery. 
