Death Ray RevisitedAs a fan of the Discovery Channel's Mythbusters I was interested to see an MIT engineering project look at Archimedes "burning glass" defense of Syracuse by using the sun to set invading Roman ships on fire, since the Mythbusters dealt with this during their 16th episode.
Reading this account and revisiting my memories of the Mythbusters account, I don't believe that anyone in either process denied the power of the Sun to create tremendous, terrestrial temperatures, it was really just a matter of reflective area and control. The key to the failure of the myth in the Mythbusters attempt and the success of the MIT attempt is in the number of mirrors, the quality of the mirrors (from polished brass to the silvered glass mirrors we use) and the aiming. After all, solar concentrators have been used to produce temperatures as high as 3200°C (5800°F)as part of energy generation systems. To give you some sense of how high this is, table salt (sodium chloride) will melt at 801°C, and in some of the solar energy collection systems they actually do use molten salt as a the medium for storing the heat in order to make use of it during the night hours and maintain power generation.
Again, a key element here, along with careful tracking of the Sun in order to keep the rays focused on the same spot, is in the number of mirrors. The temperatures I've mentioned above were the result of 2,835 sq m (about 30,515 sq ft)of mirror surface. Since Archimedes' device was described as a single, multiply-mirrored device = a sort of aimable billboard - the Mythbusters' approach was truer to the historical account. The MIT group used 127, 1 sq ft mirrors -- okay, maybe 124, since depending upon one's view two to three of the mirrors weren't on target.All in all, a fun project. I'll be curious to see if the Mythbusters - who declared the Myth "busted" based on the number of mirrors and degree of coordination necessary, at least revisit it with a footnote.
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