They say he cried, "Eureka!," leaped with glee from his bathtub, and took to the streets in the buff, still shouting. I'm somewhat skeptical of the specifics, but please read on...
Archimedes lived from about 287 BC to 212 BC, was a Greek mathematician , physicist , engineer , inventor , and astronomer . He is considered one of the greatest scientists and mathematicians of all time, though few details of his personal life are known. Among his advances in physics are the foundations of hydrostatics and statics , along with an explanation of the principle of the lever .
Archimedes is credited with designing innovative machines , including siege engines and the screw pump that bears his name. Modern experiments have tested claims that Archimedes designed machines capable of lifting attacking ships out of the water and setting ships on fire using an array of mirrors, and proved that he probably did.
One of his most famous principles is that of buoyancy, which explains why ships float, why you weigh less in the bathtub and are more buoyant in salt water than fresh. Buoyancy is an upward acting force exerted by whatever fluid opposes an object's weight. If the object is less dense than the liquid, or is shaped appropriately--as for example in a boat--the upward force will keep the object afloat. On the contrary, if the object is more dense than water, a rock for example, it will sink.
For most items, both in liquids and gasses, Archimedes' principle may be simply put: Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object. An even simpler way to say it is that buoyancy equals the weight of displaced fluid.
Perhaps the most widely known anecdote about Archimedes is that he invented a method for determining the volume of an object with an irregular shape. Supposedly, a crown had been made for King Hiero II, who had supplied the pure gold to be used. Archimedes was asked to determine whether some silver might have been substituted dishonestly by the goldsmith. Archimedes had to solve the problem without damaging the crown, so he could not melt it down into a regularly shaped body to calculate its density .
Allegedly, while taking a bath, the great scientist noticed that the level of the water in the tub rose as he got in, thus realizing that this effect could be used to determine the volume of the crown. For practical purposes water is incompressible, meaning the submerged crown would displace an amount of water equal to its own volume. Dividing the mass of the crown by the volume of water displaced, the density of the crown could be obtained. Archimedes conducted successfully, proving that silver had indeed been mixed in (his alleged "Eureka!" moment).
Since the time of this mental giant, few people have considered the possibility that a submerged object more buoyant than water--which we all know will rise to the surface, be it a cork, swim board, piece of wood, or beach ball--might rise to the surface laterally, gliding up, rather than, well, bobbing like a cork.
One person tried to work with this idea in the 1860s and actually succeeded. Amazingly, not in water, but in air! This was Dr. Solomon Andrews, of Perth Amboy, New Jersey. According to what has become almost a cult book, by John McPhee, The Deltoid Pumpkin Seed , not only did Dr. Andrews succeed, but flew himself several times in an upward gliding airship, considerably before the Wright Brothers took to the air.
Venting hydrogen, Andrews was able to descend (he had a few pounds of lift to glide him up at an angle), then throw out a few pounds of sand and glide back up. He could repeat this cycle repeatedly, until the hydrogen supply was too low. Steering was accomplished by a muslin and bamboo rudder.
Andrews is also credited with inventing the combination lock, the fumigator, cigarette filters, and about twenty-five other items (I highly recommend the book). Dr. Andrews reputation and work, in my opinion, needs to be revisited by historians, as he seems to have been lost in the cracks of history.
After reading McPhee's fascinating account of Dr. Andrews, which included work done in 1969 by the late Monroe Drew and others who tried to emulate and improve on Andrews' work, without success, I became obsessed with trying to accomplish what they were doing in air, with the difference that I would work in water. I reasoned that water behaved similarly to air, but would be far easier to experiment in, since I could use wood or Styrofoam, and typical hardware store items, such as formica, to test my ideas rather quickly. Keeping a long story short, after 5,000 designs and attempts, two years later I did strike upon an "upward gliding underwater object," and later demonstrated that the same principle did indeed work in air.
The water version is now a commercial product, as shown at http://www.aquaglider.us
The air-born version, working on the same basic principle, can be seen here: http://www.youtube.com/watch?v=9OvuVD_MqyM
The latter invention evolved into a new shape of airship, once I realized that off-the-shelf components were available to hobbyists--such as energy dense batteries, incredible remote control components, paper thin solar cells, and lighter envelope materials, among other useful items. The airborne contraptions are getting some notoriety these days and can be seen at http://www.hyperblimp.com
Credit: Many of the facts about Archimedes are from Wikipedia, slightly edited; there is considerably more info there for the interested reader.