[In honor of the forthcoming second anniversary of Dr. Boli on the World-Wide Web, Dr. Boli is reprinting a number of his own favorite articles from the past two years.]

Dear Dr. Boli: Why is the sky blue? —Sincerely, Winifred Paste-Gobble, Age 7.

Dear Miss Paste-Gobble: To answer the question you ask is more difficult than you might suppose. It requires a certain grasp of geopolitical principles and history not normally to be expected of a seven-year-old girl. Dr. Boli will therefore attempt to put the matter in the simplest possible terms, hoping that his explanation will not be too spare or sketchy for a young woman of your obvious intelligence.

For most of history, the color of the sky was the prerogative of the individual state, kingdom, or empire, and tastes have varied over the centuries. Thus from medieval paintings we can see that the sky in many European countries was formerly gold; in some, however, we see a light grey or neutral brown color, which was considered more tasteful by certain aesthetic authorities. A light grey wash was also commonly the color chosen in the Chinese Empire, although in some eras an ochre cast was preferred.

As long-distance travel became more common, there was considerable agitation for an international standard to determine the color of the sky. Sea travelers were especially inconvenienced, as, once they crossed into international waters, the sky, being under no particular jurisdiction, was simply blank.

In the middle nineteenth century, a great step was taken toward international agreement when a treaty involving most of the northern European countries and the United States of America established a single international standard for the sky over all these countries and the North Atlantic Ocean. In keeping with the technology of the time, a light cross-hatch pattern was chosen, so that it would show up well in steel engravings.

The first truly global standard for the color of the sky was promulgated by the League of Nations in 1921. The League chose a uniform dark grey; the United States, though not a member of the League, nevertheless adopted the new standard. This choice was unpopular, however, especially in the United States and Britain; and a strong grass-roots movement pushed to change the grey skies to blue, as evidenced by numerous popular songs of the period. After the Second World War, the United Nations Special Commission on Blue Skies established an international standard for a certain range of blue tones, although some local variation within that range is still permitted. The Special Commission, however, is dominated by the industrialized nations of the Northern Hemisphere, and there have been complaints that it does not adequately reflect the preferences of the global majority. Perhaps, as the formerly less developed nations grow in power and wealth, the Commission will be reconstituted to reflect greater diversity of opinion, and the standard will be revised.