Elements of the philosophy of the human mind. By Dugald Stewart. Rev. and abridged, with critical and explanatory notes, for the use of colleges and schools. By Francis Bowen ...

300 MIEMORY.
tion, which comprehends their whole contents in a single sentence: [the sine of the angle of incidence bears a constant ratio
to the sine of the angle of refraction, for each refracting medium.]
The law of the planetary motions, deduced by Kepler, from
the observations of Tycho Brahe, is another striking illustration
of the order, which an attentive inquirer is sometimes able to
trace, among the relations of physical events, when the events
themselves appear, on a superficial view, to be perfectly anomalous.
Such laws are, in some respects, analogous to the cycles
which I have already mentioned; but they differ from them in
this, that a cycle is; commonly, deduced from observations made
on physical events which are obvious to the senses; whereas
the laws we have now been considering are deduced from an
examination of relations which are known only to men of science.
The most celebrated astronomical cycles, accordingly, are of a
very remote antiquity, and were probably discovered at a period
when the study of astronomy consisted merely in accumulating
and recording the more striking appearances of' the heavens.
II. Memory aided by the power of dedutcing pcarticular truths
from general principles. — Having now endeavored to show
how much philosophy contributes to extend our knowledge of
facts, by aiding our natural powers of invention and discovery,
I proceed to explain in what manner it supersedes the necessity of studying particular truths, by putting us in possession of
a comparatively small number of general principles in which
they are involved.
I already remarked the assistance which philosophy gives to
the Memory, in consequence of the arrangement it introduces
among our ideas. In this respect, even a ltypothetical theory
may facilitate the recollection of facts, in the same manner in
which the Memory is aided in remembering the objects of
natural history by artificial classifications.*
) [" Classification is a contrivance for the best possible ordering of the
ideas of objects in our minds; for causing the ideas to accompany or suc