236 SCIENCE. 
of anthropology, give evidence of wide- 
spread interest. 
Universities are establishing special 
courses in anthropology, and teachers and 
investigators are being trained. Officers of 
anthropological museums are preparing men 
to be field workers and museum assistants. 
The public need no longer be deceived by 
accounts of giants and other wonderful dis- 
coveries. The wares of the mercenary col- 
lector are now at a discount since un- 
authentic material is worthless. 
Anthropology is now a well-established 
science; and with all this wealth of ma- 
terials and opportunities, there can be no 
doubt that in time the anthropologists will 
be able to solve that problem, which for the 
past half century bas been discussed in 
this Association—the problem of the unity 
or diversity of prehistoric man in America. 
FREDERIC WARD PUTNAM. 
HARVARD UNIVERSITY. 
THE FIELD OF EXPERIMENTAL RESEARCH.* 
PuHysIcAL research by experimental meth- 
ods is both a broadening and a narrowing 
field. There are many gaps yet to be filled, 
data to be accumulated, measurements to 
be made with great precision, but the limits 
within which we must work are becoming, 
at the same time, more and more defined. 
The upper ranges of velocities, tempera- 
tures and pressures, which manifest them- 
selves in the study of the stellar universe, 
are forever beyond the range of experiment. 
But while the astronomer must wait for op- 
portunities to observe, the experimenter 
can control his conditions and employ his 
methods and his apparatus at once to the 
question in hand. Still this work must be 
done within a certain range or must be 
limited to conditions more or less easy to 
* Address of the Vice-President and Chairman of 
Section B, Physics, before the American Association 
for the Advancement of Science at the Columbus 
meeting, August, 1899. 
[N.S. Vou. X. No. 243. 
recognize. In spite of this fact, however, 
the progress made during the past century 
is not likely to cease or abate in the next, 
and the ever-increasing number of workers. 
bodes well for the future enrichment of our 
science. 
Whatever may be our ideas of funda- 
mental entities, as expressed in various. 
theories; whether, as an example, we re- 
gard the ether as like an infinitely mobile 
fluid, or as an incompressible solid, or as a. 
jelly ; or whether we incline to think that 
being an electromagnetic medium, it may 
be without mechanical properties, which 
properties depend in some way upon the 
electromagnetic nature of the ether, we 
cannot reach sure ground without the ex- 
perimental test. 
The development in the field of research 
by experiment is like the opening of a mine, 
which, as it deepens and widens, continually 
yields new treasure, but with increased dif- 
ficulty, except when a rich vein is struck 
and worked fora time. In general, how- 
ever, as the work progresses there will be 
needed closer application and more refined 
methods. We may, indeed, find our limit. 
of depth in the mine of experiment in in- 
ordinate cost, in temperatures too high, or 
in pressures beyond the limits of our skill 
to control. 
It is but a few months since Professor 
Dewar, by the evaporation of liquid hydro- 
gen in a vacuum, closely approached, if he 
has not reached, our lower limit of possible 
temperature. Investigations of the effects 
of low temperature upon the properties of 
bodies must, from the present outlook, be 
forever limited to about 20° C. above abso- 
lute zero, unless a lighter gas than hydro- 
gen be discovered upon the earth, the actual 
existence of which it is, of course, impos- 
sible to conjecture. Before the actual ex- 
perimental demonstration of this limit the 
limit itself was known to theory, at least 
approximately, but the spur of the experi- 
