Invisible ink has a lengthy history. As early as the century AD, Pliny the Elder wrote that the sap of a tithymalus plant could be used to render a message invisible to prying eyes.

More recently, legions of schoolchildren have penned invisible messages using lemon juice. And to prove that even these days the stuff is not just a childless prank, part of the evidence that convicted Rangzieb Ahmed, an al-Qaeda operative in Britain, last year was that he had an address book with the telephone numbers of his confederates written in invisible ink.

What, though, of the opposite? Instead of something that starts off invisible and is then rendered legible (usually by the application of heat), how about a form when written is readable to begin with and then fades to invisibility?

Such an ink, suggests Bartosz Graybowski of Northwestern University in Evanston, Ill., could have all worth of applications.

The obvious one – expunging a sensitive message after a few hours, to bus and train tickets that expire automatically after – well, about a month. Graybowski thinks we have managed to make such stuff.

New item:

There are few safe places to ride out an earthquake. Surprisingly, though, a recently constructed bridge is often one of them.

Engineers have become good a designing bridges that are earthquake-resistant enough to preserve the lives of those caught crossing when a quake strikes. The problem is that the bridge is often unusable afterwards. That can hamper the activity of emergency crews as they moved around after a quake.

Mendel Saiidi of the University of Nevada, in Reno, thinks he may have found a way to keep earthquake-damaged bridges working.

He proposes to make the parts most likely to fall out of a substance called shape-memory alloy, which can “remember” what it is supposed to look like even after it has been twisted drastically out of kilter.

Dr. Saiidi gained his crucial insight by jostling models of bridges on a specially built “shake table.”

He found that, rather than failing substantially simultaneously, bridge components tend to break in a predictable order, and that the failure of one triggers the failure of the next. So, he reasoned, if the pieces that break first can be protected, the rest should never fail.

So the good doctor has developed nickel-titanium memory alloys that are superelastic. They can be distorted about 20 times as much as the steel components they replace before they reach their elastic limits.

They are expensive, but the shake tale show where they can best be deployed to keep cost down while keeping bridges up. Hooray for the good doctor!

Next item:

The law of supply and demand tells you that increasing the quality of something tends to reduce its price. But not, it seems, in higher education.

That is the puzzle on display in “Education at a Glance,” the annual research compendium published by the Organization of Economic Co-operation and Development (OECD), a Paris-based think-tank for the industrialized world. “Every year we wonder if this will be the year that higher education starts to lose its value – and very year, there is no sign of it happening,” says Andreas Schleicher, the OECD’s chief of education research.

The newly published edition shows ever more rich-world school-learners gaining higher qualifications: only a fifth in 1995 and almost twice that in 2007, the latest year the (OECD) has studied.

Mr. Schleicher says that there are already more graduates than he thought were needed on five years ago. Yet despite the vastly greater supply, employers still reward them well for the time and money they invested.

(This writer “snitched” these items from various editions of “The Economist” magazine).



Barron Mills is a former editor and publisher of The Randolph Guide. He lives in Asheboro.