bound to minute particles of ponderable matter. Here again we find
gravity-laden levity on the negative side, levity-raised gravity on the
positive.

The same language is spoken by the forms in which the luminous
phenomena appear at the two poles of a Crookes tube. Fig. i on Plate A
represents the whole phenomenon as far as such a diagram allows. Here
we see on the positive side radial forms appear, on the negative side
planar-spherical forms. As symbols of nature's script, these forms tell
us that cosmic periphery and earthly centre stand in a polar relation
to each other at the two ends of the tube. (Our optical studies will
later show that the colours which appear at the anode and cathode are
also in complete accord with this.)

At this point in our discussion it is possible to raise, without risk
of confusing the issue, the question of the distribution of the two
electric forces over the pairs of substances concerned in the
generation of electricity both by friction and in the galvanic way.
This distribution seems to contradict the picture to which the
foregoing observations have led us, for in both instances the
'sulphurous' substances (resin in one, the nobler metals in the other)
become bearers of negative electricity; while the 'saline' substances
(glass and the corrosive metals) carry positive electricity. Such a
criss-crossing of the poles-surprising as it seems at first sight - is
not new to us. We have met it in the distribution of function of the
plant's organs of propagation, and we shall meet a further instance of
it when studying the function of the human eye. Future investigation
will have to find the principle common to all instances in nature where
such an interchange of the poles prevails.