With so many scientists conducting so many experiments every year both in and out of the lab, it's not surprising that most investigations enjoy little acclaim. Every so often, though, an experiment captures the attention of scientists and laypeople alike, either because it alters our fundamental understanding of the natural world or because it reveals a solution that addresses a serious public health concern. You might think that such revelatory experiments are extraordinarily complex, and you would be right about some. But just as many are stellar examples of grace and simplicity.
In this article, we'll consider 10 of the most sublime experiments, in our humble opinion. They're organized according to the major disciplines of science -- biology, chemistry, physics and psychology -- and span more than 200 years of inquiry. In a few cases, we've paired two closely related experiments together in a single spot, not to hedge our bets, but to prove that science is a collaborative endeavor.
10: Darwin's Flowers
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You can see how the hawk moth's long proboscis (the red appendage) might suit it for pollinating a long-tubed orchid.
Most people are familiar with Charles Darwin's activities aboard the HMS Beagle and its famous journey to South America. He made some of his most important observations on the Galapagos Islands, where each of the 20 or so islands supported a single subspecies of finch perfectly adapted to feed in its unique environment. But few people know much about Darwin's experiments after he returned to England. Some of them focused on orchids.
As Darwin grew and studied several native orchid species, he realized that the intricate orchid shapes were adaptations that allowed the flowers to attract insects that would then carry pollen to nearby flowers. Each insect was perfectly shaped and designed to pollinate a single type of orchid, much like the beaks of the Galapagos finches were shaped to fill a particular niche. Take the Star of Bethlehem orchid (Angraecum sesquipedale), which stores nectar at the bottom of a tube up to 12 inches (30 centimeters) long. Darwin saw this design and predicted that a "matching" animal existed. Sure enough, in 1903, scientists discovered that the hawk moth sported a long proboscis, or nose, uniquely suited to reach the bottom of the orchid's nectar tube.
Darwin used the data he collected about orchids and their insect pollinators to reinforce his theory of natural selection. He argued that cross-pollination produced orchids more fit to survive than orchids produced by self-pollination, a form of inbreeding that reduces genetic diversity and, ultimately, survivability of a species. And so three years after he first described natural selection in "On the Origin of Species," Darwin bolstered the modern framework of evolution with a few flower experiments.
9: Decoding DNA
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Alfred Hershey in his lab in 1969
James Watson and Francis Crick get the credit for unlocking the mystery of DNA, but their discovery depended heavily on the work of others, like Alfred Hershey and Martha Chase, who, in 1952, conducted a now-famous experiment that identified DNA as the molecule responsible for heredity. Hershey and Chase worked with a type of virus known as a bacteriophage. Such a virus, made up of a protein coat surrounding a strand of DNA, infects a bacteria cell, programs the cell to make more viruses, then kills the cell to release the newly made viruses. The two knew this, but they didn't know which component -- protein or DNA -- was responsible until their ingenious "blender" experiment directed them to DNA's nucleic acids.
After Hershey and Chase's experiment, scientists like Rosalind Franklin focused on DNA and rushed to decipher its molecular structure. Franklin used a technique called X-ray diffraction to study DNA. It involves shooting X-rays at aligned fibers of purified DNA. As the X-rays interact with the molecule, they are diffracted, or bent, off their original course. When allowed to strike a photographic plate, the diffracted X-rays form a pattern that's unique to the molecule being analyzed. Franklin's famous photo of DNA shows an X-shaped pattern that Watson and Crick knew was a signature of a helical (or spiral-shaped) molecule. They could also determine the width of the helix from looking at Franklin's image. The width suggested that two strands made up the molecule, leading to the double-helix shape we all take for granted today.
8: The First Vaccination
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Costa Rica's entire population was inoculated against smallpox, measles and polio in a coordinated, countrywide campaign in 1967.
Until the stunning global eradication of smallpox in the late 20th century, smallpox posed a serious health problem. In the 18th century, the disease caused by the variola virus killed every tenth child born in Sweden and France [source: World Health Organization]. Catching smallpox and surviving the infection was the only known "cure." This led many people to inoculate themselves with fluid and pus from smallpox sores in the hopes of catching a mild case. Unfortunately, many people died from their dangerous self-inoculation attempts.
Edward Jenner, a British physician, set out to study smallpox and to develop a viable treatment. The genesis of his experiments was an observation that dairymaids living in his hometown often became infected with cowpox, a nonlethal disease similar to smallpox. Dairymaids who caught cowpox seemed to be protected from smallpox infection, so in 1796, Jenner decided to see if he could confer immunity to smallpox by infecting someone with cowpox on purpose. That someone was a young boy by the name of James Phipps. Jenner made cuts on Phipps' arms and then inserted some fluid from the cowpox sores of a local dairymaid named Sarah Nelmes. Phipps subsequently contracted cowpox and recovered. Forty-eight days later, Jenner exposed the boy to smallpox, only to find that the boy was immune.
Today, scientists know that cowpox viruses and smallpox viruses are so similar that the body's immune system can't distinguish them. In other words, the antibodies made to fight cowpox viruses will attack and kill smallpox viruses as if they were the same.
7: Proof Positive of the Atomic Nucleus
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Sometimes all it takes is a sheet of gold foil to help you figure out that atoms have a nucleus.
Physicist Ernest Rutherford had already won a Nobel Prizeradioactivity work when he began some experiments that would reveal the structure of the atom. They relied on his previous research showing that radioactivity consisted of two types of rays -- alpha and beta rays. Rutherford and Hans Geiger had determined that alpha rays were streams of positively charged particles. When he fired alpha particles at a screen, they created a sharp, crisp image. But if he placed a thin sheet of mica between the alpha-ray source and the screen, the resulting image was diffuse. Clearly, the mica was scattering some alpha particles, but how and why? in 1908 for his
In 1911, he positioned a thin sheet of gold foil, just one or two atoms thick, between the alpha-ray source and the screen. He placed a second screen by the alpha-ray source to see if any particles were being deflected straight back. On the screen behind the foil, Rutherford observed a diffuse pattern similar to the one he saw with the mica. On the screen in front of the foil, Rutherford was astonished to see that a few alpha particles bounced straight back.
Rutherford concluded that a strong positive charge at the heart of the gold atoms was deflecting the alpha particles straight back toward the source. He called this strong positive source the "nucleus," and said the nucleus must be small compared to the atom's overall size; otherwise, more particles would have bounced back. Today, we still visualize the atom as Rutherford did: a small, positively charged nucleus surrounded by a vast, mostly empty region with a few electrons.
6: X-ray Vision
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Tiny crystals ready for structural analysis by X-ray crystallography
We spoke of Rosalind Franklin's X-ray diffraction studies earlier, but her work owed much to Dorothy Crowfoot Hodgkin, one of only three women ever to win the Nobel Prize in chemistry. In 1945, Hodgkin was considered the world's foremost practitioner of X-ray diffraction techniques, so it's not surprising that she eventually revealed the structure of one of medicine's most important chemicals -- penicillin. Alexander Fleming had discovered the bacteria-killing substance in 1928, but scientists struggled to purify the chemical in order to develop an effective treatment. By mapping out the 3-D arrangement of penicillin's atoms, Hodgkin opened new avenues for creating and developing semisynthetic derivatives of penicillin, revolutionizing how doctors fought infections.
Hodgkin's field of study was known as X-ray crystallography. Chemists first had to crystallize the compounds they wanted to analyze, which was a challenge. After two different companies sent her penicillin crystals, Hodgkin then passed X-ray waves through the crystals and allowed the radiation to strike a photographic plate. As the X-rays interacted with electrons in the sample, they were diffracted slightly. This resulted in a distinct pattern of spots on the photographic film. By analyzing the position and brightness of these spots and performing numerous calculations, Hodgkin determined exactly how the atoms in the penicillin molecule were arranged.
A few years later, Hodgkin used the same technique to solve the structure of vitamin B12. She won the Nobel Prize in chemistry unshared in 1964 -- an honor that no other woman has duplicated.
5: Primordial Soup
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Harold Urey, one of the two biochemists who helped to figure out how life got started
Go back far enough in time, and you eventually have to explain how the chemicals of life -- especially proteins and nucleic acids -- formed in Earth's primordial environment.
In 1929, biochemists John Haldane and Aleksander Oparin hypothesized independently that Earth's early atmosphere lacked free oxygen. In this harsh environment, they suggested, organic compounds could form from simple molecules if they were stimulated by a strong source of energy, either ultraviolet radiation or lightning. Haldane added that the oceans would have been a "primitive soup" of these organic compounds.
U.S. chemists Harold C. Urey and Stanley Miller set out to test the Oparin-Haldane hypothesis in 1953. They reproduced the early atmosphere of Earth by creating a carefully controlled, closed system. The ocean was a warmed flask of water. As water vapor rose from the water and collected in another chamber, Urey and Miller introduced hydrogen, methane and ammonia to simulate the oxygen-free atmosphere. Then they discharged sparks, representing lightning, into the mixture of gases. Finally, a condenser cooled the gases into a liquid they collected for analysis.
After a week, Urey and Miller had astonishing results: Organic compounds were abundant in the cooled liquid. Most notably, Miller found several amino acids, including glycine, alanine and glutamic acid. Amino acids are the building blocks of proteins, which themselves are the key ingredients of both cellular structures and cellular enzymes responsible for important chemical reactions. Urey and Miller concluded that organic molecules could form in an oxygen-free atmosphere and that the simplest of living things might not be far behind.
4: Making Light
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A.A. Michelson figured out how fast light traveled with two mirrors and a little ingenuity.
When the 19th century dawned, light remained a mystery that inspired several fascinating experiments, most notably Thomas Young's "double-slit experiment" that told us light behaved as a wave, not as a particle. But we still didn't know how fast it traveled.
In 1878, physics instructor A.A. Michelson devised an experiment to calculate the speed of light and prove that it was a finite, measurable quantity. Here's what he did:
- First, he placed two mirrors far apart on a seawall near campus, aligning them so that light striking one mirror would reflect back and strike the second. He measured the distance between the two mirrors and found they were 1,986.23 feet (605.4029 meters) apart.
- Next, Michelson used a steam-powered blower to spin one of the mirrors at 256 revolutions per second. The other mirror remained stationary.
- Using a lens, he focused a beam of light onto the stationary mirror. When the light struck the stationary mirror, it bounced back toward the rotating mirror, where Michelson had placed an observation screen. Because the second mirror was moving, the returning light beam was deflected slightly.
- When Michelson measured the deflection, he found it to be 5.236 inches (133 millimeters).
- Using this data, Michelson calculated the speed of light to be 186,380 miles per second (299,949.53 kilometers per second).
The accepted value for the speed of light today is 186,282.397 miles per second. Michelson's measurement was amazingly accurate. More important, scientists had a more accurate picture of light and a foundation upon which to build the theories of quantum mechanics and relativity.
3: Revealing Radiation
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Marie Curie in her lab in 1910. Curie pretty much wrote the book on radioactivity.
The year 1897 was momentous for Marie Curie. Her first child with husband Pierre was born and, a few weeks later, she went looking for a subject for a doctoral thesis. She eventually decided to study the "uranium rays," first described by Henri Becquerel. Becquerel had discovered these rays accidentally when he left uranium salts in a dark room and returned to find that they had exposed a photographic plate. Marie Curie chose to study these mysterious rays and to determine if other elements gave off similar emissions.
Early on, Curie learned that thorium gave off the same rays as uranium. She started labeling these unique elements as "radioactive" and quickly discovered that the strength of radiationatoms of a radioactive element. By itself, this was a revolutionary discovery, but Curie wasn't done. emitted by various uranium and thorium compounds didn't depend on the compound, but on the amount of uranium and thorium present. Eventually, she would prove that the rays were a property of the
She found that pitchblende produced more radioactivity than uranium, leading her to predict that an unknown element must be present in the naturally occurring mineral. Pierre joined her in the lab, and they systematically reduced great quantities of pitchblende until they finally isolated the new element. They named it polonium after Poland, Marie's homeland. Soon after, they discovered another radioactive element, which they named radium after the Latin word for "ray." Curie won two Nobel Prizes for her work.
2: Dog Days
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Pavlov (L) owes that pooch a share of his Nobel Prize.
Did you know that Ivan Pavlov, the Russian-born physiologist and chemist responsible for the salivating-dogsblood circulation. In fact, he was studying canine digestion when he discovered what we know today as classical conditioning. experiment, wasn't interested in psychology or behavior? The research topics that interested him most were digestion and
Specifically, he was trying to understand the interaction between salivation and the action of the stomach. Pavlov had already noted how the stomach wouldn't start digesting without salivation occurring first. In other words, reflexes in the autonomic nervous system closely linked the two processes. Next, Pavlov wondered if external stimuli could affect digestion similarly. To test this, he began flashing a light, ticking a metronome or sounding a buzzer at the same time he offered food to his research dogs. In the absence of these external stimuli, the dogs only salivated when they saw and ate their food. But after a while, they began to salivate when stimulated with external lights or sounds, even when food wasn't present. Pavlov also found that this type of conditioned reflex dies out if the stimulus proves "wrong" too often. For example, if the buzzer sounds repeatedly and no food appears, the dog eventually stops salivating at the sound.
Pavlov published his results in 1903. A year later, he won a Nobel Prize in medicine, not for his work with conditioning, but "in recognition of his work on the physiology of digestion, through which knowledge on vital aspects of the subject has been transformed and enlarged" [source: Nobelprize.org].
1: Authority Figures
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Stanley Milgram proved that people would turn that knob pretty high if an authority figure told them to.
Stanley Milgram's 1960s obedience experiments qualify as some of the most famous and controversial science experiments. Milgram wanted to know how far ordinary people would go in delivering painful shocks to a peer, when commanded to do so by a scientific authority. This is his experiment:
- Milgram recruited volunteers -- ordinary residents -- to deliver the shocks. He recruited actors to be the subjects who would receive the shocks. The final player was the authority figure, a scientist who would remain in the room for the study's duration.
- The authority figure began each experiment by showing the unknowing volunteer how to use the mock shock machine. The machine allowed volunteers to deliver up to 450 volts, a shock labeled as highly dangerous.
- Next, the scientist told the volunteers they were testing to see how shocks might improve word association recall. He instructed the volunteers to shock learners (actors) for wrong answers and to raise the voltage as the experiment progressed.
- The learners cried out whenever they received a shock. At about 150 volts, they would demand to be freed. The scientist encouraged volunteers to continue delivering shocks no matter how agitated the learners became.
- Some volunteers stopped at about 150 volts, but most kept going until they reached the maximum shock level of 450 volts.
Many people questioned the ethics of the experiments, but the results were fascinating. Milgram showed that average people will inflict a lot of pain on an undeserving victim simply because an authority commands them to do so.
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