the collection and description of facts, the precise statement of
what is the case. Observation and measurement are here indispen-
sable. But it is at this level, too, that experimentation plays its
part. The purposes for which experiments may be devised are mul-
tiple. They may be simply a part of the procedure of determining
the case; but they may also be designed as tests for hypotheses
or for the verification or disproof of laws. That experimentation
implies its own set of assumptions of a logical and ontological
nature may be remarked only in passing.

Facts ascertained by observation and/or by experimentation
become the basis for inductive generalizations and, ultimately, for
the construction of explanatory hypotheses. Such hypotheses--
although they are essentially imaginative constructions of logical
schema from which laws descriptive of the observed facts, can be
derived by logical transformations--must be logically possible
(i.e., they must be self-consistent) and must have predictive signi-
ficance.

Now, the history of science is quite clear on one point: facts
were discovered, isolated, and described in various fields of in-
vestigation; and explanatory hypotheses were developed corre-
spondingly. Thus, there was the field of classical mechanics and
the field of electrodynamics, and there was also the quite separate
field of chemistry. Each field was developed independently, and in
each field explanatory hypotheses made possible the derivation
of specific laws descriptive of the observed facts. That all the facts
were, in essence, the results of measurements and were statable in
purely quantitative terms was but a result of certain assumptions
underlying the enterprise in all fields of investigation.

But when facts were discovered which legitimately belonged
to more than one field of investigation--to classical mechanics,
for example, as well as to electrodynamics--it was found neces-
sary to construct a theory ( Einstein's theory of relativity) whose
definitions and postulates made possible the logical derivation of
laws in both fields. And, similarly, new definitions and assump-
tions, entailing the law of quantum mechanical resonance, led to
the integration of the whole realm of physics and the realm of

-2-