. From the first movement
in the primary ether to solid substances, such as wood or iron or our own
flesh, is thus a series of vibrations in a succession of mediums, each
denser than the preceding one out of which it was concreted and from which
it receives the vibratory impulse. This is in effect what physical science
has to tell us. But to get further back we must look into the world of the
invisible, and it is here that psychological study comes to our aid. We
cannot, however, study the invisible side of Nature by working from the
outside and so at this point of our studies we find the use of the
time-honored teaching regarding the parallelism between the Macrocosm and
the Microcosm. If the Microcosm is the reproduction in ourselves of the
same principles as exist in the Macrocosm or universe in which we have our
being, then by investigating ourselves we shall learn the nature of the
corresponding invisible principles in our environment. Here, then, is the
application of the dictum of the ancient philosophy, "Know Thyself." It
means that the only place where we can study the principles of the
invisible side of Nature is in ourselves; and when we know them there we
can transfer them to the larger world around us.

In the concluding chapters of my "Edinburgh Lectures on Mental Science" I
have outlined the way in which the soul or mind operates upon the physical
instrument of its expression, and it resolves itself into this--that the
mental action inaugurates a series of vibrations in the etheric body which,
in their turn, induce corresponding grosser vibrations in the molecular
substance until finally mechanical action is produced on the outside. Now
transferring this idea to Nature as a whole we shall see that if our mental
action is to affect it in any way it can only be by the response of
something at the back of material substance analogous to mind in ourselves;
and that there is such a "something" interior to the merely material side
of Nature is proved by what we may call the Law of Tendency, not only in
animals and plants, but even in inorganic substances, as shown for instance
in Professor Bose's work on the Response of Metals. The universal presence
of this Law of Tendency therefore indicates the working of some
non-material and, so to say, semi-intelligent power in the material world,
a power which works perfectly accurately on its own lines so far as it
goes, that is to say in a generic manner, but which does