24 
secutive order of the universe, it will be necessary to consider 
a little the meaning of that word cause , which I have used more 
than once with reference to its contemporaneous order. For 
there is no part of Nature, as regarded by Science, from which 
the idea of causation can be excluded, although, strictly, it 
implies a succession of events. And as much confusion of 
thought is often introduced into this subject of causation, 
through ambiguity in the use of the word, it will be well to 
call attention to certain facts in this part of our general 
subject which may assist in guiding us. The word cause , in 
reference to the phenomena of Nature, for example, is popu- 
larly used in more than one sense. Some of these phenomena 
are, we know, in a greater or less degree, subjective. An image 
in a looking-glass, and the rainbow as an arch in the sky, are 
purely subjective forms. They are effects produced on the 
eye of the beholder in a certain position by light, — in one in- 
stance proceeding from a certain object and reflected in the 
mirror ; in the other, proceeding from the sun and reflected 
in drops of water. In these cases. Science examines and 
determines the causes of the phenomena ; that is, the reasons 
why they are to us such as they are. The explanation is a 
geometrical one, and may be represented by a figure. Colour, 
again, is subjective in a different sense. There is that in 
Nature (viz., the different lengths of the light undulations) 
which is the external cause of the sensations of colour, 
although the sensation itself is purely subjective. Science 
proceeds a step further in the succession of physical causes by 
the explanation now generally accepted, viz., that in the 
retina there are three kinds of nerve-fibres, the excitations of 
which give respectively the sensations of red, green, and 
violet ; the combinations of these in different proportions pro- 
ducing the sensations of every shade of colour. But the 
cause of the colour-sensations being produced by these nerves, 
or of the union of sensations of red and green (for example) 
being yellow, science cannot explain. It must be observed 
that, in every process of causation, there are really three 
elements, — the antecedent, the consequent, and the reason of 
the sequence. And the causation is completely known only when 
all three are known. When, as we shall find is the case with 
physical energies, the consequent is the continuance of the 
antecedent in another form, the whole causation is explained. 
But this Science cannot prove to be the case in the transition 
from a physical impression to a sensation.* 
* "When we pass from the objective to the subjective, from the non ego to 
the ego, sometimes, as in the case of colour, there is no congruity whatever 
