As tour guides of medieval cathedrals like to point out, centuries-old stained-glass windows are often thicker at their bottoms than at their tops. The commonly cited reason is that glass is not really a solid material: rather, glass is technically a highly viscous liquid. The difference in the thickness of the windows, according to this theory, results from the stained glass slowly flowing downward under the pull of gravity.
Alas, that is a myth, says researcher Edgar Dutra Zanotto of the Federal University of Sao Carols in Brazil. Working from knowledge of the physical properties of the glass, he calculated how long it would take for glass to flow enough to change visibly. His conclusion was that cathedral glass would need many billions of years, "well beyond the age of the universe".
The real reason may be very mundane: the difference in thickness could be either a feature or a defect in 12th-century glass-manufacturing techniques.
Tossed in space
Since the beginning of the space age, rockets have launched more than 20,000 metric tons of material into orbit. Today 4,500 tons remain there in the form of nearly 10,000 "resident space objects". The extra-terrestrial refuse comes in many forms: dead spacecraft, discarded rocket bodies, remnants of satellite break-ups, launch- and mission-related cast-offs, solid-rocket exhaust, even droplets from leaking nuclear reactors. Radar observations reveal an estimated 300,000 pieces larger than 4mm. And the amount of space junk keeps on increasing.
Most spacecraft are still at little risk of impacts during their operational lifetimes (although on average the space shuttle, must have one in eight of its windows replaced after each mission because of collisions with tiny bits of space trash). And the space environment in the future is likely to be less benign.
Although spacefaring countries recognise the problem, they have yet to decide collectively what should be done and who should police the situation. Individual space agencies are nonetheless striving to create less garbage. And to protect new orbital objects from junk already up in space, designers are now building spacecraft with shields that can protect against multiple strikes of objects 1cm in diameter. The new International Space Station will feature such shields around its habitable compartments, fuel lines, control gyroscopes and other sensitive areas.
With all the advances toward equality for women, one might assume that there are many female programmers. But according to statistics compiled by Tracy K Camp, assistant professor of computer science at the University of Alabama, the number of undergraduate degrees in computer science awarded to women is shrinking steadily, both in real numbers and as a percentage of degrees awarded.
Why the drop? According to one survey, computer games tend to be male- oriented, giving boys more computer experience. The long hours typical of programming jobs, the gender discrimination, the lack of role models and the antisocial image of the hacker have also tended to steer women away. And sexual harassment is perceived to be higher in the computer industry than in other fields. Proposals for change include making existing female role models more visible, improved mentoring and encouraging equal access to computers for schoolgirls.
! All items are adapted from 'Scientific American' magazine. Copyright 1998, Scientific American, Inc. Visit the 'Scientific American' website at www.sciam.com. All rights reserved