NOVEMBER 12, 1897. ] 
automatically, although todo so we must move 
it in a direction exactly contrary to what the 
image seems to require. 1 
Now, Dr. Stratton’s experiment goes one step 
farther. In this, not only an object, but the 
whole external world, including the visible parts 
of the body, are inverted. Not only some, but 
all our movements must be readjusted. The 
results are certainly surprising and may possi- 
bly require some reconstruction of fundamental 
conceptions of space—how much I am not pre- 
pared to say, but they certainly do not affect 
the law of direction properly understood. 
The law of direction gives nothing but the 
direction of the impressing force, and this it gives 
always. Under normal conditions, 7. e., when 
the light comes straight, and without deviation 
from the object to the eye, it gives the true 
places of objects and radiants, and therefore 
upright vision ; but not under abnormal condi- 
tions of deviation of the light. For example, 
we look at an object in a mirror inclined 45° to 
the line of sight. The apparent object is seen 
far away, 90°, fromitstrue place; but this does 
not violate the law of direction, but confirms it. 
We see in the direction of the impressing force, 
which in this case—in all cases—is the last 
direction of the light. Again, in gazing at an 
object through a microscope, we see it inverted, 
i. e., the radiants are seen in wrong places. 
But this does not violate the law of direction. 
We still see every radiant in the direction of 
the impressing force, but that direction has been 
changed so as to give wrong places. 
So in Dr. Stratton’s experiment. At first, at 
least, we see things in wrong places, 7. e., wrong 
as judged by the deliverances of other senses, 
but yet in strict accordance with the law of di- 
rection, 7. e., in the direction of the impressing 
force. As to the final result of an indefinite 
continuance of these experiments and whether 
complete accord in the deliverances of all the 
senses would ever be reached, so that things 
would again seem natural as they do now, this 
seems to me a question of philosophy rather 
than science, or, perhaps, I should say of psy- 
chology rather than physiology. I am not now 
concerned with it. 
But it must be clearly understood that the 
law of direction is purely a formal law, 7. e., a 
SCIENCE: 
( 
, 
739 
law which groups consistently all the facts con- 
cerning the relative places and positions of ob- 
jects in the external world as we know it. This 
is all that it pretends to do. The discovery 
and announcement of such general formule is 
the main function of science. As to what the 
external world is, and what space and direction 
are, that is another matter. These more am- 
bitious questions belong to philosophy, not to 
science. 
In conclusion, I have said that the law of di- 
rection is inherited, not acquired. By this I do 
not mean that in the last analysis it is not due 
to experience. It does, indeed, come from ex- 
perience, but not mainly from individual experi- 
ence. Itis the result of ancestral experience, 
inherited all along the line of evolution ever 
since eyes were formed, and finally embodied in 
brain structure. 
JOSEPH LE CONTE. 
BERKELEY, October 11, 1897. 
WHEN an author replies to a reviewer it is 
but courteous for the latter to try to show that 
he has not been careless in his statements. 
1. Professor Le Conte’s statement (page 78), 
‘T believe that the existence of the central spot 
is necessary to fixed, thoughtful attention, and this 
again in its turn is necessary for the develop- 
ment of the higher faculties of the mind,’’ I un- 
derstood to refer both to individual develop- 
ment and to race evolution. The limited field 
of distinct vision and the associated eye-move- 
ments seem to me factors or correlates in the 
evolution of attention, but by no means 
‘necessary.’ That is a dangerous word to 
apply to nature, which works in many ways. 
Most men may be ‘visuals’, but some of us are 
‘motiles’; the horse is an ‘audile,’ the dog an 
‘olefactor’?. Asa matter of fact, Professor Le 
Conte makes a mistake in stating that the 
‘central spot * * * exists only in man and in 
the higher monkeys’ with a foot-note to the 
effect that in different forms it is found in some 
birds. Knox in 1823 described the central spot 
and fovea in lizards and they have been found 
in fishes by Carriére, Krause and others. A 
central spot, 7. e., an area of acute vision, has 
been described in nearly all mammals, though 
the fovea is probably only present in the pri- 
