Great IdeasNature and science
Experiment and observation
Testing ideas against the world instead of only arguing about them.
The question
Why test ideas instead of only arguing about them? How did people learn to ask nature questions with experiments?
How the books answer
Oldest first. Each stop is our own short summary of what the author argued; follow the link to the rung for the whole lesson.
c. 350–322 BC
Aristotle, History of Animals, Parts of Animals, Motion and Gait of Animals, Generation of Animals
Aristotle was a great observer. He opened eggs day by day to watch chicks grow and gathered reports from fishermen and farmers. He did not do controlled experiments as we know them, but he insisted on checking theory against what we see.
late 2nd century AD
Galen, On the Natural Faculties
Galen did real experiments. To show that the kidneys make urine, he tied the tubes leading from them to the bladder in a living animal and watched what happened. He scolded rivals who argued without testing.
1600
William Gilbert, On the Loadstone and Magnetic Bodies
Gilbert says the old books are full of untested claims about magnets. He tests them himself, rubbing magnets with garlic and showing nothing changes. He calls for true experiments in place of guesses and fables.
“Plutarch and Claudius Ptolemy, and all the copyists since their time, think that a loadstone smeared with garlick does not allure iron.”
1620
Francis Bacon, Novum Organum
Bacon argues that knowledge grows by planned experiments and careful tables of cases, not by clever argument alone. He warns that we notice cases that fit our ideas and forget the ones that don't. Experiments should be designed to catch our mistakes.
“The former like ants only heap up and use their store, the latter like spiders spin out their own webs.”
1628; the letters On the Circulation of the Blood, 1649
William Harvey, On the Motion of the Heart and Blood in Animals, and On the Circulation of the Blood
Harvey ties tight and loose bands on an arm to show which way blood flows in arteries and veins. He presses on veins to show the valves only let blood go toward the heart. Simple experiments anyone could repeat made his case.
Go to the rung: Harvey: On the Motion of the Heart and Blood
1638
Galileo Galilei, Dialogues Concerning the Two New Sciences
Galileo rolls balls down a smooth grooved ramp many times and times them carefully. He repeats the test at different slopes and finds the same law. An experiment, for him, is a question asked of nature in the language of mathematics.
1647–1654
Blaise Pascal, Treatises on the vacuum, the equilibrium of liquids and the weight of the air, and the arithmetical triangle
Pascal designs experiments with tubes of mercury and water to test whether nature abhors a vacuum. The test on a mountain shows the air's weight holds up the mercury. He says the ancients would have changed their minds if they had seen it.
“But if the modern experiments had been known to them, perhaps they would have found cause for affirming what they found cause for denying, for the reason that vacuum had not yet appeared.”
1704
Isaac Newton, Optics
Newton passes sunlight through one prism, picks out a single color, and sends it through a second prism. The color bends again but does not change. This crucial experiment showed that colors are in the light, not made by the glass.
“The Light of the Sun consists of Rays differently Refrangible.”
1832–1855
Michael Faraday, Experimental Researches in Electricity
Faraday kept careful numbered notes of thousands of experiments. After many failures, he found that a current appears only when a magnet moves or a current switches on or off. He wrote his results so clearly that others could repeat them.
“But whilst the voltaic current was continuing to pass through the one helix, no galvanometrical appearances of any effect like induction upon the other helix could be perceived.”
Go to the rung: Faraday: Experimental Researches in Electricity
For young readers
An experiment is a test to find out if an idea is true. Instead of just saying 'I think heavy things fall faster,' you drop two things and watch!
A good experiment changes only one thing at a time. Want to know if plants need light? Grow two bean plants the same way, but put one in a dark closet. What happens after a week?
Talk about it
- Why is it better to test an idea than just argue about it?
- Gilbert tested whether garlic stops magnets. Can you test an old saying, like 'a watched pot never boils'?
- Why should an experiment change only one thing at a time?
- Faraday kept careful notes. Why do scientists write everything down?
- Plan an experiment together. What will you change, and what will you measure?
Where else on the site
- Hypotheses and Controlled Experiments
- Designing Experiments
- Observational Studies and Experiments
- Observing Like a Scientist
- Magnets and Magnetic Fields
- Faraday's Law
Every rung tagged with this idea:
- Aristotle: The Animals
- Hippocrates: On Medicine
- Galen: On the Natural Faculties
- Gilbert: On the Loadstone
- Bacon: Novum Organum
- Bacon: New Atlantis
- Harvey: On the Motion of the Heart and Blood
- Galileo: Two New Sciences
- Harvey: On the Generation of Animals
- Pascal: The Scientific Treatises
- Newton: Optics
- Lavoisier: Elements of Chemistry
- Faraday: Experimental Researches in Electricity
- Darwin: The Origin of Species
These pages are our own short synthesis, written for families. They were inspired by Mortimer J. Adler's Syntopicon, the index of great ideas in volumes 1 and 2 of Great Books of the Western World, but the questions, summaries and groupings are ours, not the Syntopicon's. Short excerpts come from public-domain translations, credited where they appear.