Methuselah trusts and the magic of compound interest

"Methuselah trusts" are (very) longterm trusts that accumulate so much compound interest over hundreds of years that by the time they mature, they could potentially pose a real threat to the economy. That's why they're illegal. From Lapham's Quarterly:

 Wikipedia Commons Thumb 9 9C Compound Interest.Svg 600Px-Compound Interest.Svg
Hartwick College didn’t really mean to annihilate the U.S. economy. A small liberal-arts school in the Catskills, Hartwick is the kind of sleepy institution that local worthies were in the habit of founding back in the 1790s; it counts a former ambassador to Belize among its more prominent alumni, and placidly reclines in its berth as the number-174-ranked liberal-arts college in the country. But along with charming buildings and a spring-fed lake, the college once possessed a rather more unusual feature: a slumbering giant of compound interest.

With bank rates currently bottomed out, it’s hard to imagine compound interest raising anyone much of a fortune these days. A hundred-dollar account at 5 percent in simple interest doggedly adds five bucks each year: you have $105 after one year, $110 after two, and so on. With compound interest, that interest itself get rolled into the principal and earns interest atop interest: with annual compounding, after one year you have $105, after two you have $110.25. Granted, the extra quarter isn’t much; mathematically, compound interest is a pretty modest-looking exponential function.

Modest, that is, at first. Because thanks to an eccentric New York lawyer in the 1930s, this college in a corner of the Catskills inherited a thousand-year trust that would not mature until the year 2936: a gift whose accumulated compound interest, the New York Times reported in 1961, “could ultimately shatter the nation’s financial structure.” The mossy stone walls and ivy-covered brickwork of Hartwick College were a ticking time-bomb of compounding interest—a very, very slowly ticking time bomb.

"Trust Issues" (Thanks, Jason Tester!)