528 
combination of two lenses to produce ach- 
romatism, and Huygens with his discover- 
ies and explanations’ of double refraction 
and polarization; while in the meantime 
Roemer had measured the velocity of light. 
All these accessions crowded one another 
so closely that the emission theory of New- 
ton and the undulatory theory of Huygens 
followed almost as a matter of necessity. 
The battle royal of these two rival theories, 
as you know, lasted for nearly a century, 
until the emission theory, by the sheer 
force of critical observations and experi- 
ments, was displaced by the undulatory 
theory through the brilliant researches of 
Young and Fresnel. 
When we turn from the physical to the 
geological and biological sciences, the same 
lessons of the necessity and the efficiency 
of observation and experiment are still 
more strikingly apparent. For although 
geology and biology are the youngest of the 
grand divisions of science, they have accom- 
plished more than all others toward giving 
man a proper orientation with respect to 
the rest of the universe. Geology as we 
now understand the term is but little more 
than a hundred years old, and biology, in 
the sense now attached to the word, is less 
than fifty years old. Nevertheless, these 
sciences have been the chief contributors to 
the doctrine of evolution, which, in view of 
the wide range of its applicability, must be 
regarded as the most important generaliza- 
tion of science. 
It is a singular circumstance, however, 
considering the early advances made in the 
interpretation of the phenomena of astron- 
omy, that the equally ubiquitous and far 
more accessible phenomena of geology and 
biology should have been so tardily investi- 
gated. The cause of this delay seems to 
lie in the fact, not without examples in the 
present day, that our remote ancestors had 
the habit of constructing their theories first 
SCIENCE. 
[N. S. Von. XIII. No. 327. 
and making their observations, if at all, 
afterwards; and in the cases of geology 
and biology they were so well satisfied with 
their theories that the trouble of making 
observations was for a long time dispensed 
with. 
We of the present day have no right, 
perhaps—and I for one would not be dis- 
posed to use such a right if conceded—to 
blame our predecessors for the narrow, and 
in some instances crooked, views they held 
with regard to these subjects. But on the 
other hand, we shall fail, I think, to inake 
proper use of our opportunities if we do not 
learn speedily to conduct scientific investi- 
gations in the future so as to avoid such 
colossal blunders as mar the history of geol- 
ogy and biology from its beginnings down 
almost to our own time. 
As an illustration of the blunders re- 
ferred to I may cite the profound reluc- 
tance, even of eminent men of science, to ac- 
cept the plainest teachings of observation 
with respect to geological time up to the 
middle of the century just passed. Not 
until Lyell, the great champion of uniform- 
itarianism as opposed to catastrophism, 
had published his ‘ Principles’ (1830) did 
scientific opinion show a tendency to ac- 
cept the fact-of the hoary age of the earth, 
everywhere attested by the rocks in her 
crust. 
And what a storm of opposition and con- 
demnation, amounting almost in some 
cases to social ostracism, was visited by the 
very ‘salt of the earth’ against those who 
ventured during the sixties and the seven- 
ties of the last century to consider favorably 
the arguments of the ‘ Origin of Species’ ! 
All this has about it the freshness, and pos- 
sibly the pain and the humor, of personal 
recollection for those of us who are old 
enough to have lived in two epochs. That 
a mistake of this sort could have been 
made thirty or forty years ago seems 
strange enough in these peaceful times of 
