202 W. L. COURTNEY, M.A., LL.D., 
come before us, they will come and go without leaving any 
trace, or communicating any data to our stock of mental 
acquisitions. But elementary though Attention may be, it is, 
notwithstanding, very difficult to explain its functions and 
its character. Psychologically, Attention seems due to a 
more or less conscious effort of mind which is directed to the 
more striking characteristics of the sensations which come 
before it. But again, there is nothing so capricious as 
Attention. Sometimes we by no means attend to the merely 
striking characteristics, but to any chance quality which for 
some reagon or other engages us, to the exclusion of other 
qualities. Sometimes, again, Attention is apparently habitual 
or only semi-conscious; at other times, it appears impossible 
without a serious volitional effort. But, though we may 
labour to explain Attention psychologically, it is a far harder 
task for the physiologist. If all mental conditions were the 
material result. or effect of molecular agitation within the 
nerves, it is very difficult to say why some forms of nervous 
agitation should produce “Attention,” while other forms exactly 
similar, so far as their material character goes, should fail to 
vet themselves registered within the brain. We are looking 
upon some scene or landscape, or, to talk a scientific language, 
various nerve messages are proceeding from the end-organs 
of sense, which have been excited by external stimuli: we 
attend to some features in this landscape; we notice a 
particular tree, or figure, or colour, not always because it is 
striking, but for some capricious fancy of ours. How can 
this be, if there be not a mind within us, with laws of its 
own, which has indeed a nervous mechanism, but is not the 
slave of the mechanism? Otherwise, one would think that 
all nerve-messages ought either to have equal values or to 
stimulate attention in equal proportion to their vividness— 
neither of which is the case. The only law, itself somewhat 
doubtful, is Weber’s Law, which may be expressed as follows: 
Some ratio, although quantitatively different, is believed 
to exist for every sense. That is to say, itis true of every 
sense that not every change in objective stimulus occasions 
a change in subjective sensation, but that every change in 
stimulus must bear a certain definite ratio (varying in the 
different senses) to the already existing stimulus, betore the 
intensity of the sensation, as a conscious state, changes. 
Differently stated, not absolute stimuli are felt, but only 
relative. 
It is all very well to tell us that the seat of 
attention and concentration lies in the motor centres 
