Reading Comprehension

Radio communication in aviation is deliberately impoverished, and the poverty is the point. Controllers and pilots use a restricted vocabulary with prescribed word order, pronounce digits in a fixed manner, and repeat back the instructions they receive so that the sender can hear whether the message survived the journey. The discipline exists because the channel is poor: transmissions overlap, accents differ, static intrudes, and a listener who expects a particular instruction will often hear it whether or not it was sent. The collision of two large airliners on a runway in fog at Tenerife in 1977, still the deadliest accident in aviation, turned on exactly this weakness, since an ambiguous phrase about takeoff meant one thing to the crew that transmitted it and something else to the controller who heard it. The lesson drawn was not that the people involved were careless but that ordinary language is too flexible for a channel this fragile. Phraseology was tightened afterward, and certain words were reserved for one meaning alone. The readback is the other half of the defense, because it makes a misunderstanding audible to a third party while there is still time to correct it. Neither measure removes the danger, but together they convert a private error into a public one.

The convoy system reduced the ocean from an expanse in which every ship was a separate target to a small number of moving points. Those points still had to be found and defended, and the submarine remained elusive because a boat on the surface is a very small object against a very large sea. Aircraft changed that arithmetic in two ways, for a patrol aircraft searches in an hour an area that a surface escort could not cover in a day. Its mere presence also forced a submarine to submerge, which cut its speed so severely that it could no longer maneuver into position ahead of a convoy. For much of the war a stretch of the mid-Atlantic lay beyond the radius of aircraft flying from either shore, and the losses concentrated there in a way that made the cause unmistakable. Closing that stretch required nothing new in principle: long-range aircraft assigned to the task rather than to bombing, small carriers sailing with the convoys themselves, and airborne radar that could find a surfaced boat at night. When those measures arrived together in 1943, the exchange turned within a few months, and the campaign that had been the gravest threat to Allied supply was brought under control.

A government's budget responds to the business cycle even when lawmakers change nothing. When the economy slips into recession, incomes and profits fall, so income and payroll tax receipts shrink, while spending on programs such as unemployment insurance rises as more people qualify for benefits. The deficit widens as a result, and the added spending and lighter taxes help cushion the fall in household purchasing power. When the economy recovers, the process runs in reverse: receipts climb, benefit claims fall, and the deficit narrows without any new legislation. Economists call these features automatic stabilizers because they tend to moderate swings in demand without waiting for a political decision. The same features complicate the reading of any single year's budget. Budget analysts, including those at the Congressional Budget Office, therefore estimate what the deficit would have been had the economy been operating at its potential, separating the cyclical part of the deficit from the structural part that persists in good times and bad. A deficit that is large mainly because of a recession tells a different story about fiscal policy than one of the same size in a year of full employment.

One of the world's great insurance markets grew out of a London coffee house rather than out of any deliberate plan. Edward Lloyd opened his establishment near the Port of London in the late seventeenth century, and because it drew ship captains, merchants and shipowners, he made a business of gathering and circulating reliable shipping news. Men with capital to risk met there to insure voyages, and their customary procedure gave the trade a lasting word. A broker wrote the details of a ship and its cargo on a slip of paper, and each backer willing to accept part of the risk signed his name beneath them, along with the share he would bear, until the whole value was covered. These underwriters were individuals staking their own fortunes, so a single wreck could ruin a careless one, while a prudent one limited his exposure by taking small portions of many different voyages. The informal gathering eventually became a formal society with rules for its members, yet it kept the principle that the market is a place where independent backers meet rather than a single company that issues policies. That distinction still separates Lloyd's from the ordinary insurer, which accepts risks in its own name and pays claims from its own funds.

Before the late 1950s, published measurements of carbon dioxide in the air varied so widely that many scientists doubted the gas had any stable background level. Charles David Keeling, then a young chemist in California, built an instrument precise enough to settle the question and found that air sampled in remote places on calm afternoons gave nearly the same value wherever he collected it. The scatter in the older records, he concluded, came largely from local sources such as cities, forests and soils, which enrich or deplete the air close to the ground. With support from the International Geophysical Year, he began continuous measurements in 1958 at an observatory high on the slopes of Mauna Loa in Hawaii, far from continental sources of contamination. Within a year the record showed a regular seasonal rhythm, with the concentration falling during the northern summer, when growing vegetation withdraws carbon dioxide, and rising again in winter, when decay releases it. The swing is larger at stations farther north, where land plants dominate, and much weaker near the South Pole, where the seasons of plant growth have little direct influence. Superimposed on that rhythm was a steady climb from one year to the next, and after several years it could no longer be attributed to instrument drift or chance. The combined pattern, a sawtooth rising decade after decade, became known as the Keeling curve, and it remains the longest direct record of carbon dioxide in the atmosphere.