While browsing, I came across this article. I am posting it here. For more details refer to the book "The top ten most beautiful experiments" by George Johnson. 1. Galileo Galilei
Period:- (1564 to 1642)
Legend has it that in order to test how gravity worked, Galileo dropped two balls, a heavy one and a light one, from the Leaning Tower of Pisa, showing that they landed at the same time. Historians doubt this - because his actual experiment was much better.
The Italian carved a groove down the centre of a board about 20 feet long and 10 inches wide. Then he propped it at an angle and timed how quickly the balls rolled down the track. What he discovered was that the distance the ball travels is proportional to the square of the time that has elapsed.
But how, in an age before clocks, could Galileo measure this so precisely? He probably used music. Along the ball's path, he placed cat-gut frets, like those on a lute. As the rolling ball clicked against the frets, Galileo sang a tune, using the upbeats to time the motion and discover a new law.
2. William Harvey
Period:-(1578 to 1657)
Galen had taught that the body contains two separate vascular systems: a blue "vegetative" fluid, the elixir of nourishment and growth, coursed through the veins, while a bright red "vital" fluid travelled through the arteries, activating the muscles and stimulating motion. Invisible spirits, or "pneuma", caused the fluids to slosh back and forth like the tides. The heart just went along for the ride, expanding and contracting like a bellows.
Harvey was dubious. Cutting open a snake, he used a forceps to pinch the main vein, or vena cava, just before it entered the heart. The space downstream from the obstruction emptied of blood, while the heart grew paler and smaller, as though it were about to die. When Harvey released the grip, the heart refilled and sprung back to life.
Pinching the heart's main artery had the opposite effect: the space between heart and forceps became gorged with blood, inflating like a balloon. It was the heart, not invisible spirits, that was the driving motor, pushing red blood to the extremities of the body, where it passed into the bluish veins and returned to the heart for rejuvenation. There was one kind of blood and it moved in a circle: it circulated.
3. Isaac Newton
Period:-(1642 to 1727)
In Newton's day, Europe's great scientists believed that white light was pure and fundamental. When it bounced off a coloured object or passed through a tinted liquid or glass, it became stained somehow with colour - whatever "colour" was.
Newton, holed up in a dark room at his family farm in Woolsthorpe, turned the idea on its head. He cut a hole in his window shutter and held a prism in the path of the sun, spreading the light into an oblong spectrum. Then he funnelled the spectrum through a second prism. White again.
Finally, he allowed the colours to pass, one by one, through the second prism. Starting at the red end and progressing toward the blue, each colour was bent a little more by the glass. Light, Newton had discovered, "consists of rayes differently refrangible". It was white that was the mongrel - not just another colour, but a combination of them all, a "heterogeneous mixture of differently refrangible rayes".
4. Antoine-Laurent Lavoisier
Period:-(1743 to 1794)
In the 18th century, the conventional wisdom was that things burned because they contained something called phlogiston. Set a piece of wood on fire and it exuded this mysterious essence, leaving behind a pile of ash. Wood, it logically followed, was composed of phlogiston and ash.
Likewise, heating a metal under an intense flame left a whitish brittle substance, or calx. Metal was thus composed of phlogiston and calx. But Lavoisier was troubled by one thing: with the phlogiston expelled, the calx was heavier than the original metal. How could phlogiston weigh less than zero?
By cooking mercury in a flask, he showed that, as the calx formed, something was sucked from the surrounding air. He isolated the gas and lit a taper, noting that it burned "with a dazzling splendour". Calx was not metal without phlogiston, but metal combined with what Lavoisier would name oxygen.
Left behind in the flask was a gas that extinguished flames - what we now call nitrogen. Fire and rust produced similar reactions. Lavoisier had discovered the nature of oxidation - and the chemical composition of the air.
5. Luigi Galvani
Period:-(1737 to 1798)
One day in Bologna, Galvani was startled to see a dismembered frog's leg twitch when an assistant cranked a static electricity generator on the far side of the laboratory. The same effect occurred during lightning storms. Even more remarkably, Galvani found, the frog's leg would move, seemingly of its own accord, as it hung from a hook, even in the clearest weather.
He concluded that some kind of animal electricity was involved. His compatriot Alessandro Volta was just as sure that the electricity was non-biological, produced by the touching of two different metals: the frog's leg had hung on a brass hook from an iron rail.
Though neither man could quite see it, they were dancing around a single truth. Volta confirmed that electricity can indeed come from two metals - he had invented the battery. But Galvani went on to show that there is also electricity in the body.
Taking a dissected frog, he nudged a severed nerve against another using a probe made of glass. No metal was involved, but when nerve touched nerve, the muscle contracted, as surely as if someone had closed a switch.
6. Michael Faraday
Period:-(1791 to 1867)
In his youth, Faraday had performed a suite of experiments showing the linkage between electricity and magnetism, inventing, along the way, the electric motor and the dynamo. But by the time he was 53, he had fallen into a deep depression.
Maybe it was a barrage of flirtatious correspondence from Lady Ada Lovelace, the daughter of Byron, that snapped him out of his funk: whatever the cause, he decided to push the unification a step further, and show that electricity and magnetism are related to light.
Using an Argand oil lamp, Faraday projected polarised light through a block of glass, alongside of which sat a powerful electromagnet. Holding a polarising filter, called a Nicol prism, to his eye, he rotated it until the light was extinguished. Then he switched on the current.
The image of the flame suddenly reappeared. He turned the magnet off and the flame disappeared. The magnetic field, he realised, was twisting the light beam - and if the polarity of the field was reversed, the light beam rotated the other way. Faraday had unified two more forces, demonstrating that light was actually a form of electromagnetism.
7. James Joule
Period:-(1818 to 1889)
Lavoisier had done away with phlogiston, but before his death he had introduced the idea of caloric, his name for an invisible substance - a "subtle fluid" - said to be the carrier of heat.
Put a metal poker in a fire, he argued, and the caloric will rise up the shaft until you can feel the warmth in the handle. According to this theory, the reason something gets hot when you rub it is because you abrade the surface and let some caloric out.
But why, no matter how long you rubbed, did the heat keep coming? Either there was an infinite supply of caloric in every object or, as Joule suspected, heat was something else altogether. With a rigging of pulleys and weights, he spun a paddle wheel inside a vessel of water and carefully measured the change in temperature.
The motion of the paddle made the water warmer, and the relationship was precise: raising one pound of the liquid by one degree took 772 foot-pounds of work. Joule had discovered that heat was not a thing. It was a form of motion.
8. A A Michelson
Period:-(1852 to 1931)
For a Navy man such as Michelson, it was unthinkable that the Earth could be adrift in the infinitude with no landmarks to measure by. So he set out to prove the existence of the aether, the fixed backdrop of the universe and the substance in which our planet swam as it moved through space. In his apparatus, two beams of light travelled in perpendicular directions.
The beam moving upstream - with the earth's orbit - should, he predicted, be slowed by the wind of the aether, while the other beam should be less effected. By comparing their velocities with an interferometer, Michelson would calculate the motion of the Earth against the heavens.
But something was wrong: the speed of the two beams was the same. With help from Edward Morley, Michelson made the measurements much more precisely. Still there was not a hint of aether. In fact, the experiment was a beautiful failure.
As Einstein went on to show, there can be no fixed space or even fixed time. As we move through the universe, our measuring sticks shrink and stretch, our clocks run slower and faster - all to preserve the one true standard, which is not the aether, but the speed of light.
9. Ivan Pavlov
Period:-(1849 to 1936)
Contrary to legend, Pavlov hardly ever used bells in his experiments with salivating dogs. His animals were more discriminating. In his "Tower of Silence", sealed from distractions, he and his assistants conditioned the animals to distinguish between objects rotating clockwise or counter-clockwise, between a circle and an ellipse, even between subtle shades of gray.
But for his most remarkable experiment, he used music. First, a dog was trained to salivate when it heard an ascending scale, but not a descending one. But what, Pavlov wondered, would happen if the animal listened to the other combinations of the same notes? The melodies were played and the spittle collected.
Through simple conditioning, the dog had categorised the music it heard into two groups, depending on whether the pitches were predominantly rising or falling. The mind had lost a bit of its mystery, Pavlov had shown how learning was a matter of creatures forming new connections in a living machine.
10. Robert Millikan
Period:-(1868 to 1953)
By bending a cathode ray with an electrical field, Cambridge scholar J?J Thomson had shown electricity to be a form of matter, and measured the ratio of its charge to its mass. It followed that electricity was made of particles, but to clinch the case someone needed to isolate and measure one.
In Millikan's laboratory in Chicago, two round brass plates, the top one with a hole drilled through the centre, were mounted on a stand and illuminated from the side by a bright light. Then the plates were connected to a 1,000-volt battery. With a perfume atomiser, Millikan sprayed a mist of oil above the apparatus and watched through a telescope as some of the droplets - they looked like little stars - fell into the area between the plates.
As he tweaked the voltage, he watched as some drops were pushed slowly upward while others were pulled down. Their passage through the atomiser had ionised them, giving the drops negative or positive charges.
By timing their movement with a stopwatch, Millikan showed that charge, like pocket change, came in discrete quantities. He had found the electron.
Top left is Venus, Top right is Jupiter, Bottom center is moon
