The Blackwell Guide to the Philosophy of Science - The Department ...

Herschel (discoverer of Uranus) draws a useful distinction between them. Observation,
he says, is a matter of
noticing facts as they occur without any attempt to influence the frequency of their
occurrence . . . (Herschel, 1966, p. 76)
It can be likened to passively
listen[ing] to a tale, told us, perhaps obscurely, piecemeal, and at long intervals of
time, with our attention, more or less awake (p. 77) [where in many cases the] . . .
tale is told slowly and in broken sentences (p. 78).
Experiment, by contrast, is a matter of
Experiment and Observation
putting in action causes and agents over which we have control, and purposely varying
their combinations, and noticing what effects take place (Herschel, p. 76)
Herschel likens this to cross-examining a
witness and by comparing one part of his evidence with the other, while he is yet
before us . . . reasoning upon it in his presence [so that we can] . . . put pointed and
searching questions, the answer to which may at once enable us to make up our
minds (Herschel, 1966, pp. 66, 77).
In experiments, natural or artificial systems are studied in artificial settings
designed to enable the investigators to manipulate, monitor, and record their
workings, shielded, as much as possible from extraneous influences which would
interfere with the production of epistemically useful data. Investigators who
cannot produce the data they need in this way can sometimes rely on “experiments
of nature.” That’s the term Bernard used in connection with diseases which
provided evidence for the study of the physiology of the affected organs and
systems (Bernard, 1949, p. 10). Like observable instances of astronomical
regularities, experiments of nature are interactions in which natural mechanisms
conspire, without contrivance by the investigators, to produce effects of interest
to the investigator. Obtaining and interpreting data from such occurrences sometimes
involves enough equipment and elaborate arrangements to blur Herschel’s
distinction. (Eddington’s use of eclipse photographs to calculate the deflection of
starlight is an example (Dicke, 1964, p. 2).)
But even so, there are epistemically significant differences between observing
without interfering, and setting up an experiment, altering its components, and
intervening in their workings as needed to investigate the significance of the data
the experiment produces. Medical research can dramatize this point. Suppose a
hideous disease is observed more frequently in people who eat certain foods than
in people who do not. It may not be at all obvious from the statistical distribution
of these and other observed factors whether the diet and the disease are con-
129