292 
about electric and magnetic forces, but I 
mean that we do know enough about such 
forces to have a clear notion of their varia- 
tion in space and their variation in time. 
This feature of the ideal model or de- 
scription seems to me to be necessary in 
order to make the model acceptable as the 
ultimate or last attainable explanation of 
phenomena. The elements of which the 
model is constructed must be of types 
which are immediately perceived by the 
senses and which are accepted by every- 
body as the ultimate data of consciousness. 
It is only out of such elements that an 
explanation, in distinction from a mere 
barren set of formulas, can be constructed. 
A description of phenomena in terms of 
four dimensions in space would be unsatis- 
factory to me as an explanation, because by 
no stretch of my imagination can I make 
myself believe in the reality of a fourth 
dimension. The description of phenomena 
in terms of a time which is a function of 
the velocity of the body on which I reside 
will be, I fear, equally unsatisfactory to 
me, because, try I ever so hard, I can not 
make myself realize that such a time is con- 
ceivable. 
Tried by this test, I feel that the prin- 
ciple of relativity does not speak the final 
word in the discussion about the structure 
of the universe. The formulas which flow 
from it may be in complete accord with all 
discovered truth, but they are expressed in 
terms which themselves are not in harmony 
with my ultimate notions about space and 
time. That this is true is so evident that it 
is generally admitted. Some writers say 
that we should not let this cireumstance 
disturb us, because Kant has said that time 
and space are mere forms of perception, a 
scheme in which we must arrange occur- 
rences so that they may acquire objective 
significance. I do not altogether under- 
stand what Kant meant by this, but I am 
SCIENCE 
[N.S. Vou. XXXV. No. 895 
sure he did not mean that by the exercise 
of our wills we can violently eject from our 
consciousness the notions of space and time 
which we have in common with the whole 
race of man, and impose on ourselves other 
and radically different notions. Planck 
compares our position before the new no- 
tions presented by the theory of relativity 
to the position of the medieval peoples 
before the notion of the antipodes. It 
seems to me that there is no real similarity 
between the two positions. Many men in 
the Middle Ages believed that there were 
no antipodes, but their belief was based on 
reasons, and so far were they from being 
unable to conceive of antipodes and to be- 
lieve in their existence, that there were 
men who actually maintained their exist- 
ence, and were pursued therefor as here- 
tics. I do not believe that there isany man 
now living who ean assert with truth that 
he can conceive a time which is a function 
of velocity or is willing to go to the stake 
for the conviction that his ‘‘now’’ is an- 
other man’s ‘‘future’’ or still another 
man’s ‘‘past.”’ 
One of the members of this society, 
recognizing our present inability to con- 
ceive of relative time, and conceiving our 
intuitions of space and time to be the result 
of heredity operating through many gen- 
erations of men who lacked the light of 
relativity, once proposed to me that every 
one who could get even a glimmer of the 
notion of relative time should persistently 
exercise his mind therein and teach it to his 
students, in the hope that in a few genera- 
tions the notion would emerge with the 
force of an intuition. It would not be fair 
to leave the impression that he was sol- 
emnly serious when he made this sugges- 
tion. When Matthew Arnold was asked to 
endure the transliteration of Greek names 
into English in order that the new forms 
might become familiar to future scholars, 
