Why do the spouters on some water fountains produce two streams of water that merge into one before reaching your parched lips? Why not just one stream to start with? --Steven Palkovitz, Alexandria, Virginia

In an age when you can't even fix your Chevy without having to contend with microchips, Cecil is always cheered by examples of low-tech ingenuity. The twin-stream water fountain is a perfect example. But first we need to put things in proper historical perspective. Let me quote from a brochure for Halsey Taylor water fountains, one of the leading names in the industry:

"In 1896, Halsey W. Taylor lost his father to an outbreak of typhoid fever caused by a contaminated water supply. This personal tragedy led the young Halsey Taylor to dedicate his life to providing a safe, sanitary drink of water in public places. . . . The historic Double Bubbler(TM) projector was designed by Halsey Taylor himself, and still ranks as the most important innovation in the industry's history. It projects two separate streams of water, which converge to provide an abundant 'pyramid' of water at the apex of the stream. This gives the user a fuller, more satisfying drink."

The folks at Halsey Taylor are being polite here. What they mean is that the Double Bubbler enables you to take in more water and less air when you drink. As a result, you don't burp. Think of all the delicate social negotiations you've been involved in that have gone awry because of an ill-timed belch. Had you been drinking from a Double Bubbler, that fat contract (job, bimbo, whatever) might have been yours.

The Double Bubbler serves other purposes as well. You get less spraying, presumably because the water slows down when the two streams merge. The double streams also act as a sort of pressure regulator. If the water pressure is unusually strong one day, a single-stream fountain might give the unwary sipper a shot in the eye. When the twin streams of the Double Bubbler meet, however, their upward momenta tend to cancel each other out no matter how high the pressure gets.

One last thing. You know how kids like to hold their thumbs over the bubbler to make the water spray all over the room? Halsey Taylor fountains have an "antisquirt groove" consisting of a slot cut through the bubbler head just below the tip. If some wisenheimer puts his thumb over the tip to try to make the fountain squirt, the water merely dribbles harmlessly out the sides through the antisquirt groove--a drag if you're a rambunctious sixth-grader, but a gift from God if you're anybody else.

BATTLE OF THE DECADES, PART TWO

Cecil, you fell into an ignorant trap trying to claim the '90s won't start until 1991 [September 14, October 19]. Let's take it from the top. The first decade AD started in the year 1; the second began in year 11. Time marched on. People acknowledged that the 5th century, the fifth set of 100 years since 1 AD, began in 401 AD, the 11th century in 1001, etcetera. But one day somebody started talking about, oh, the "1300s." Linguistically, this is a very different term from "14th century." It refers to the set of a hundred years designated 1300 to 1399. The 1300s include the year 1300, even though 1300 is the last year of the 13th century. Complicated, but I'm sure you can understand the foolishness of trying to claim 1300 isn't in the 1300s.

The same reasoning applies to decades. I will grant you that the 200th decade AD will not begin until 1991. But "decade" refers to a ten year period. Any ten year period. Webster's New Collegiate Dictionary defines the sixties as "the years 60 to 69 in a lifetime or century." If someone tells you they live in New York "in the East Sixties," you wouldn't expect them to live on 70th Street, would you? The '90s (and the 1900s) will end as the year 2000 begins. But the 20th century will still have a year to go. --John Cork, Los Angeles

Oh, piffle. There's no point being a columnist if you can't be obstinate in the face of all logic. But if you're determined to stick to this silly idea that "the 80s" means all the years with eightysomething in their names, be my guest.