12 PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND. 
objective reality of Space and Time, as explained in the 
well-known and oft-quoted Scholium, does not affect the 
adequacy of this system as a means of description. 
Again, the Aither provides a convenient means of 
describing electromagnetic phenomena, but the description 
is equally satisfactory whether we regard the Atther as 
a mental concept or, alternatively, as an entity having real 
objective existence. 
It is certainly true that Natural Science as such has 
no concern with Metaphysics, but we must take care to 
give the correct meaning to the assertion. Metaphysical 
questions may be safely ignored as unsolved but irrelevant ; 
it is dangerous to avoid them by a tacit and unconscious 
assumption of a particular solution. A besetting sin of 
the scientific worker is a tendency to assume a realist 
solution of metaphysical problems; and the tendency is all 
the more dangerous in that it is unconscious. 
Consider, for example, the idea of space. By a process 
of abstraction from observations of material bodies the 
idea is developed and refined until we have the full concept 
of a three-dimensional continuum, subject to the laws of 
Euclidean Geometry, in which material bodies exist. By 
a metaphysical assumption this is endowed with objective 
reality and immediately certain consequences follow; 
among others, displacements are combined by the parallelo- 
gram law and length becomes an intrinsic absolute property 
of material bodies. These are spoken of as facts of experi- 
ence; whereas they are actually the outcome of experience 
combined with certain metaphysical assumptions. Our 
direct experience indicates that length is a relation between 
object and observer which changes with change of relative 
position, but we introduce our assumptions about space 
and, by correcting for change of position, attribute absolute 
length to the object. 
Now nothing is gained by this tendeney towards 
realism; absolute length as a fact of experience is of no 
more value in scientific work than absolute length as a 
convenient interpretation of experience. On the other 
hand much flexibility is lost; if we accept absolute length 
as fact we are limited in our interpretation of further 
experience, if we look upon it as interpretation we can 
modify that interpretation as further experience demands. 
