Google modestly declares its mission "to organize the world's information and make it universally accessible and useful." But convenience may be part of the problem. In the Web's early days, the most serious search engine was AltaVista. To use it well, a searcher had to learn how to construct a search statement, like, say, "Engelbert Humperdinck and not Las Vegas" for the opera composer rather than the contemporary singer. It took practice to produce usable results. Now, thanks to brilliant programming, a simple query usually produces a first page that's at least adequate -- "satisficing," as the economist Herbert Simon called it.

The efficiency of today's search engines arises from their ability to analyze links among Web sites. Google led in ranking sites by how often they are linked to other highly ranked sites. It did so using an elaborate variation of a concept familiar in natural science, citation analysis. Instead of looking at which papers are cited most often in the most influential journals, it measures how often Web pages are linked to highly ranked sites -- ranked by links to themselves.

Citation analysis has been attacked in library circles for inflating the ratings (and indirectly the subscription prices) of certain journals. Search engines have the opposite problem: dispersion rather than concentration of interest. Despite constant tweaking, their formulas display irrelevant or mediocre sites on a par with truly expert ones.

Curious about the academic field of world history? A neophyte would find little help entering "world history" in Google. When I tried, the only article on the world history movement, from the open-source Wikipedia project, didn't appear until the fifth screen and was brief and eccentric, erroneously dating the field from the 1980's. (In fairness to Wikipedia, that entry has since been corrected and improved; moreover, the paid-access Encyclopaedia Britannica site has no specific article at all.) Only on the seventh screen did I find the World History Network site, financed by the National Endowment for the Humanities, and it is not yet a good portal for beginners.

Many students seem to lack the skills to structure their searches so they can find useful information quickly. In 2002, graduate students at Tel Aviv University were asked to find on the Web, with no time limit, a picture of the Mona Lisa; the complete text of either "Robinson Crusoe" or "David Copperfield"; and a recipe for apple pie accompanied by a photograph. Only 15 percent succeeded at all three assignments.