326 
for the minimum requirements for 
achieving a long and trackless journey 
are a clock and a compass. 
It is curious, and perhaps significant, 
that, on a small scale, both these 
senses are connected in human expe- 
rience with the ear (auditory and non- 
auditory parts of the labyrinth). It is 
notorious that the visual mechanism 
is capable of only an elementary appre- 
ciation of time interval. Ifa man de- 
sires to appreciate the time interval 
between two events he either turns 
the time interval into a space inter- 
val by some stroboscopic or oscillo- 
graphic device for visual observation 
or he arranges for each event to give 
an audible signal and listens to the 
interval; and the second method is, 
within a limited range, surprisingly 
sensitive. 
On a short scale, too, the normal 
orientation mechanism of the semi- 
circular canals and utricle in the non- 
auditory part of the labyrinth tells 
man not only which way up he is in the 
absence of visual clues but which way 
he is turning and how fast. We have, 
therefore, in the ear and its associated 
centers in the brain the rudiments of 
the clock and compass we were looking 
for. 
It is true that these rudiments are 
very inadequate. They do not hinder 
civilized man from losing his way in a 
fog, nor prevent him from estimating 
quite wrongly the time he spends in a 
dentist’s chair or a tavern. It may, 
however, be that they are vestiges 
rather than rudiments. There are 
people who can awake themselves at 
a specified hour without an alarm 
clock. There are people, generally 
country folk, in whose lives the points 
of the compass are a constant frame 
of reference. The Irishwoman in the 
railway carriage in Somerville’s story 
“Poisson d’Avril,” who said ‘‘Move 
west a small piece, Mary Jack, if you 
please. I declare we’re as throng as 
three in a bed this minute,” is a type 
of an aptitude so common as to be the 
rule in many districts. 
Because we know so little about these 
ANNUAL REPORT SMITHSONIAN INSTITUTION, 1948 
“senses” it is still possible to adopt 
either of two radically different theo- 
retical approaches. The sense of time 
has been regarded as a sense of inter- 
val, for which the reference standard 
is the solar day. And alternatively, 
the reference standard has been 
thought to be inherent and associated 
in some way with the rate of living 
of the animal organism. The latter 
view would make the time sense inde- 
pendent of external stimuli, at least in 
the warm-blooded birds or animals, 
and would make biological time akin 
in a philosophic sense to the thermo- 
dynamic time of Eddington and Milne. 
In a rather similar way the sense of 
direction and position has been re- 
garded as either the expression of a 
kind of dead reckoning for which the 
starting point is a particular orienta- 
tion in a known topography or as 
being based on some kind of internal 
compass needle. Ising (1945) has 
made the interesting suggestion that 
the semicircular canals may be inher- 
ently suited to supply the internal 
compass needle since they are a device 
by which Coriolis forces might be dis- 
tinguished from other and generally 
much larger forces acting on a bird 
in flight. The physics involved is in 
a field which is unfamiliar to most 
people. Any body which moves at 
constant velocity over the earth’s sur- 
face will in general have a component 
of velocity toward the earth’s axis of 
rotation and will in consequence ex- 
perience a horizontal force normal to 
its own direction of motion. This is 
the Coriolis force. It is proportional 
to the velocity component toward the 
earth’s axis and is therefore zero at 
the Equator and also for movement 
in east or west direction. For north 
or south movement it is a maximum 
and increases with latitude. 
If the body which we have been 
considering were a bird in level flight 
at constant speed, the Coriolis force 
would be equivalent, so far as the 
bird’s receptors were concerned, to a 
very small linear acceleration side- 
ways, and there would be no way of 
