SEPTEMBER 22, 1899. ] 
tution of matter and the connecting ether? 
How are we to look upon the explanations 
they afford? Are we to put atoms and ether 
on an equal footing with the phenomena 
observed by our senses, as truths to be in- 
vestigated for their own sake? Or are they 
mere tools in the search for truth, liable to 
be worn out or superseded ? 
That matter is grained in structure is 
hardly more than the expression of the 
fact that in very thin layers it ceases to be- 
have as in thicker layers. But when we 
pass on from this general statement and 
give definite form to the granules or assume 
definite qualities to the intergranular ce- 
ment, we are dealing with pure hypotheses. 
Itis hardly possible to think that we shall 
ever see an atom or handle the ether. We 
make no attempt whatever to render them 
evident to the senses. We connect ob- 
served conditions and changes in gross visi- 
ble matter by invisible molecular and ethe- 
real machinery. The changes at each end 
of the machinery of which we seek to give 
an account are in gross matter, and this 
gross matter is our only instrument of de- 
tection, and we never receive direct sense 
impressions of the imagined atoms or the 
intervening ether. To astrictly descriptive 
physicist their only use and interest would 
lie in their service in prediction of the 
changes which are to take place in gross 
matter. 
It appears quite possible that various 
types of machinery might be devised to pro- 
duce the known effects. The type we have 
- adopted is undergoing constant minor 
changes, as new discoveries suggest new 
arrangements of the parts. Is it utterly 
beyond possibility that the type itself 
should change? 
The special molecular and ethereal ma- 
chinery which we have designed, and which 
we now generally use, has been designed 
because our most highly developed sense 
is our sense of sight. Were we otherwise, 
SCIENCE. 
391 
had we a sense more delicate than sight, 
one affording us material for more definite 
mental presentation, we might quite pos- 
sibly have constructed very different hy- 
potheses. Though, as we are, we cannot 
conceive any higher type than that founded 
on the sense of sight, we can imagine a 
lower type, and by way of illustration of 
the point let us take the sense of which my 
predecessor spoke last year—the sense of 
smell. In us itis very undeveloped. But 
let us image a being in whom it is highly 
cultivated, say, a very intellectual and very 
hypothetical dog. Let us suppose that he 
tries to frame an hypothesis as to light. 
Having found that his sense of smell is 
excited by surface exhalations, will he not 
naturally make and be content with a cor- 
puscular theory of light? When he hag 
discovered the facts of dispersion, will he 
not think of the different colors as different 
kinds of smell—insensible, perhaps, to him, 
but sensible to a still more highly gifted, 
still more hypothetical dog ? 
Of course, with our superior intellect and 
sensibility, we can see where his hypothesis 
would break down; but unless we are to 
assume that we have reached finality in 
sense development, the illustration, gro- 
tesque as it may be, will serve to show that 
our hypotheses are in terms of ourselves 
rather than in terms of Nature itself, they 
are ejective rather than objective, and so 
they are to be regarded as instruments, 
tools, apparatus only to aid us in the search 
for truth. 
To use an old analogy—and here we can 
hardly go except upon analogy—while the 
building of Nature is growing spontaneously 
from within, the model of it, which we seek 
to construct in our descriptive science, can 
only be constructed by means of scaffolding 
from without, a scaffolding of hypotheses. 
While in the real building allis continuous, 
in our model there are detached parts which 
must be connected with the rest by tem- 
