Today, a young student forms a scientific theory.
The University of Houston's College of Engineering
presents this series about the machines that make
our civilization run, and the people whose
ingenuity created them.
I found a remarkable sentence
Jane Marcet's early- nineteenth-century
textbook, Conversations on Vegetable
Physiology. In it, a fictional tutor, Mrs. B.,
talks with two pupils, Emily and Caroline. The
conversation has turned to the question of how
plants take nourishment from sap. Mrs. B. says,
"Many ingenious hypotheses have been proposed
but none have proved satisfactory."
Then she adds,
That which appears least objectionable, is the
agency of Electricity; but it must be owned that
the chief argument in favour of [it] is that we are
not yet sufficiently acquainted with its powers to
[disprove] the hypothesis.
That says a lot about how scientific thinking goes
wrong. Marcet warns her young pupils how tempting
and dangerous it is to accept an explanation simply
because it's mysterious. Theories alone will no
more explain anything than bare data will. We need
both. I think about the science-fiction writer who
creates time travel by sending a space ship through
a worm hole. Worm holes are mysterious enough to
accommodate anything, so why not time travel?
Electricity was a cutting-edge scientific mystery
back in 1829. The science of Marcet's age had
become a science of data and observation. A whole
set of new theoretical sciences was about to
replace all that. Soon thermodynamics, field
theory, molecular theory, and germ theory would be
the new concept-driven sciences.
While most scientists around Marcet still reached
for laundry lists of data, her books breathed forth
a keen sense of those emerging theoretical,
idea-based, sciences. She has Emily and Caroline
trading, not just facts, but ideas about
When Mrs. B. explains that hot air over the Sahara
has a high capacity for absorbing moisture, Emily
says, "Oh, that must be why North winds seldom
bring rain. They hold more of their moisture as
they move from the North into warmer lands to the
South." It's hard to teach students to make
theoretical deductions like that. It's far easier
to let science look like laundry lists of canned
So Marcet's books, written in England,
became a staple of American science
education. Our early educators wrestled with them.
They had the sense to use her books, but
they fought with the content. The exercise
questions they added looked for words and phrases,
not for deductions. The footnotes they added
criticized her use of theory. Yet they chose her
books instead of the many available texts that
simply recited facts.
Marcet nurtured students' minds by emphasizing
theory and experiments over applications. No wonder
she issued that warning about sweeping unexplained
nature under the rug of mysterious electricity.
When you're teaching concepts, and not just
outcomes, you'd better point out the traps.
Teaching students to trust their own ability to
think is a dangerous business if we don't teach
them to think clearly.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
Marcet, J. H., Conversations on Vegetable
Physiology; Comprehending the Elements of Botany,
with their Application to Agriculture. New York:
Printed by Sleight & Robinson, 1830.
Lindee, M. S., The American Career of Jane Marcet's
Conversations on Chemistry, 1806-1853. Isis,
March, 1991, pp. 9-23.
Moon, H. C., The Career of Jane Marcet: A
Reflection of Forces that Shaped Women's place in
19th century Science. A Thesis Presented to the
Faculty of the Honors College and the Department of
History, Univesity of Houston, August 1995.
For more on Marcet see Episodes 741, 744,
745, 828, 950
An illustration from Marcet's Vegetable
The Engines of Our Ingenuity is
Copyright © 1988-1999 by John H.