Natural Philosophy 179The more widely accepted, the system of imponderables, associated each
of the main divisions of physica particularis—light, heat, magnetism, elec-
tricity—with a special fl uid or fl uids composed of weightless or unweigh-
able particles that repelled and / or attracted one another and the particles
of ponderable matter. Although the fl uid(s) associated with different sets
of phenomena did not interact, they had this much in common besides
imponderability: the forces acting between their particles were central
distance forces of the type that Newton had invoked in his gravitational
theory. The system rested precariously on a few measurements like Cou-
lomb’s on electric and magnetic forces and more securely on a formidable
array of analogies among electricity, heat, radiant heat, and light.^16
The other integrating system bruited around 1800 was the Naturphil-
osophie of F. W. J. Schelling, which, insofar as it took in all of nature and
marginalized experiment and mathematics, was a throwback to 1700 and
even earlier times. But, like the old global natural philosophy, it soon
moved to exploratory experimentation and realized some fi ne discoveries.
It achieved its greatest successes with the battery that Alessandro Volta—
one of the great acrobats on the network of imponderables—made public
in 1800, just after Schelling had set the basis of his speculative physics.
Like Cartesianism, Naturphilosophie rested on a priori premises and was
intended to be true of nature. In this last respect it again differed from the
system of imponderables, whose advocates admitted freely that they did
not know even in the exemplary case of electricity whether its effective
cause was two fl uids, one fl uid, or none.^17 An instrumentalist attitude to-
ward theory often accompanies quantifi cation. Mixed mathematics may
be precise, but, as Aristotle knew, there is no truth in it.
- Natural Philosophers
The character of natural philosopher is more diffi cult to set forth than
the nature and periods of natural philosophy. A common escape, which
makes natural philosophers “practitioners” of natural philosophy, will not
do. “Practitioner” has too much the air of “professional,” as in “general
practitioner.” Johnson gives clergymen and idolaters (“papistical practitio-
ners”) as examples. He also allows the use of the term for an “exercised,
thorough- paced practitioner of... vices,” or anyone else who does some-
thing habitually.^18 Although some eighteenth- century people practiced
natural philosophy as an art or profession and others used it to practice
upon the gullible, most who claimed the title natural philosopher did not
consider natural philosophy a vocation. In 1718 the Royal Society asked
its members to identify their interests, “to show what all are good and