When Do Fish Sleep? Part 15

Why Are There Lights Underneath the Bottom Steps of Escalators and Why Are They Green?

Those emerald lights are there to outline the periphery of the step on which you are about to hop or hop off. The majority of accidents on escalators occur when a pa.s.senger missteps upon entering or exiting the escalator. The lights, which are located just below the first step of ascending stairs (and the last step of descending stairs), are there to show the way for the unproficient escalator pa.s.senger.

Escalator lights are green for the same reason that traffic lights use green: Green is among the most visually arresting colors.

Submitted by John T. Hunt of Pittsburgh, Pennsylvania.

Why Are Rented Bowling Shoes So Ugly?

We know that taste in art is a subjective matter. We are aware that whole books have been written about what colors best reflect our personalities and which colors go best with particular skin tones.

But on some things a civilized society must agree. And rented bowling shoes are ugly. Does anybody actually believe that maroon-blue-and-tan shoes best complement the light wood grain of bowling lanes or the black rubber of bowling b.a.l.l.s?

Bruce Pluckhahn, curator of the National Bowling Hall of Fame and Museum, told us that at one time "the black shoe-like the black ball-was all that any self-respecting bowler would be caught dead using." Now, most rented bowling shoes are tricolored. The poor kegler is more likely to be dressed like Cindy Lauper (on a bad day) than Don Carter.

We spoke to several shoe manufacturers who all agreed that their three-tone shoes were not meant to be aesthetic delights. The weird color combinations are designed to discourage theft. First, the colors are so garish, so ugly, that n.o.body wants to steal them. And second, if the rare pervert does try to abscond with the shoes, the colors are so blaring and recognizable that there is a good chance to foil the thief.

Of course, rented bowling shoes get abused daily. A bowling proprietor is lucky if a pair lasts a year. Gordon W. Murrey, president of bowling supply company Murrey International, told Imponderables that the average rental shoe costs a bowling center proprietor about $10 to $25 a pair. The best shoes may get rented five hundred times before falling apart, at a very profitable $1 per rental.

Even if rentals were a dignified shade of brown, instead of black, tan, and red, they would get scuffed and bruised just the same. Bowlers don't expect fine Corinthian leather. But can't the rented bowling shoes look a littler cla.s.sier, guys? Isn't a huge 9 on the back of the heel enough to discourage most folks from stealing a shoe?

Submitted by Shane Coswith of Reno, Nevada.

What's the Difference Between Virgin Olive Oil and Extra Virgin Olive Oil?

We promised ourselves that we wouldn't make any jokes about virgins being hard to find and extra-virgins being impossible to find, so we won't. We will keep a totally straight face while answering this important culinary Imponderable.

We may have trouble negotiating arms reductions, but on one issue the nations of the world agree; thus, the International Olive and Olive Oil Agreement of 1986. This agreement defines the terms "virgin olive oil" and "extra virgin olive oil."

Any olive oil that wants to call itself virgin must be obtained from the fruit of the olive tree solely by mechanical or other physical means rather than by a heating process. The oil cannot be refined or diluted, but may be washed, decanted, and filtered.

The lowest grade of virgin olive oil is semi-fine virgin olive oil, which is sold in stores as "virgin." This oil must be judged to have a good flavor and no more than three grams of free oleic acid per hundred grams of oil.

The next highest grade, fine virgin olive oil, cannot exceed one and a half grams of oleic acid per hundred grams and must have excellent taste.

Extra virgin olive oil must have "absolutely perfect flavour" and maximum acidity of one gram per hundred grams. According to Jose Luis Perez Sanchez, commercial counselor of the Emba.s.sy of Spain, extra virgin olives are often used with different kinds of natural flavors and are quite expensive, which any trip to the local gourmet emporium will affirm.

As with many other food items, the prize commodity (extra virgin olive oil) is the one that achieves quality by omission. By being free of extraneous flavors or high acidity, the "special" olive oil is the one that manages what wouldn't seem like too difficult a task: to taste like olives.

Submitted by Phyllis M. Dunlap of St. George, Utah.

Why Are There Cracks on Sidewalks at Regular Intervals? What Causes the Irregular Cracking on Sidewalks?

Believe it or not, those regularly s.p.a.ced cracks are there to prevent the formation of irregular cracks.

We tend to see concrete as lifeless and inert, but it is not. Concrete is highly sensitive to changes in temperature. When a sidewalk is exposed to a cool temperature, it wants to contract.

Gerald F. Voigt, director of Engineering-Education and Research at the American Concrete Pavement a.s.sociation, explains that concrete is very strong in compression but only one tenth as strong in tension.

It would be much easier to break a piece of concrete by pulling on two opposite ends, rather than push it together. Cracking in concrete is almost always caused by some form of tensile development.

In many cases the concrete slabs are restricted by the friction of the base on which they were constructed. This frictional resistance will put the slabs in tension as they contract; if the resistance is greater than the tensile strength of the concrete, a crack will form. Something has to give.

Without any form of restraint, the concrete will not crack.

Concrete tends to shrink as it dries, and tends to gain strength over time. Thus, sidewalks are most vulnerable to cracking the first night after the concrete is placed. Two strategies are employed to combat cracking.

Arthur J. Mullkoff, staff engineer at the American Concrete Inst.i.tute, told Imponderables that properly positioned reinforcing steel is often used to reduce cracks. But the most effective method of minimizing cracks is to predetermine where the cracks will be located by installing joints in between segments of concrete.

Those s.p.a.ces that threaten the well-being of your mother's back are a form of "tooled joints," strategically positioned cracks. These joints are placed in all types of concrete slabs. Gerald Voigt elaborates: The concrete is sawed or tooled to approximately one-quarter of the thickness of the slab, which creates a "weakened plane." The concrete will crack through the "weakened plane" joint, because that joint is not as strong. As you can see on almost any sidewalk, tooled joints are placed about every four to eight feet. These joints are placed to control where cracks develop and avoid random cracking which is usually considered unattractive.... Typically sidewalks are four inches thick; joint depth must be at least one-quarter of the sidewalk thickness.

Perhaps the most surprising element in the story of concrete cracks is that although so much effort is put into preventing them, cracks are not particularly troublesome. The National Ready-Mixed Concrete a.s.sociation says that cracks rarely affect the structural integrity of concrete. Even when the cracks are wide enough to allow water to seep in, "they do not lead to progressive deterioration. They are simply unsightly."

Incidentally, our correspondent asked how the superst.i.tion "Step on a crack, break your mother's back" originated. We've never found a convincing answer to this Imponderable, but Gerald Voigt offered a fascinating theory: Since a concrete sidewalk consists of many short segments (slabs) of white concrete, it can be imagined that it is like a human spine. The spine also consists of many short segments (vertebrae) of white bones. The weak links in each system are the joints. Stepping on a sidewalk crack, or joint, is a.n.a.logous to stepping on the weakest area of the spine. I imagine if I were walking down a spine, I would avoid stepping on a vertebrae link, wouldn't you?

Submitted by Mrs. Harold Feinstein of Skokie, Illinois. Thanks also to Henry J. Stark of Montgomery, New York.

Why Do We Have to Shake Deodorant and Other Aerosol Cans Before Using?

If you could see inside a can of deodorant, you would see that the ingredients are not arranged uniformly in the can. The propellant is not soluble and so won't mix with the active ingredients in the deodorant.

In many cases, you would see three or four levels of ingredients in a can. The top layer would contain the hydrocarbon gas used as a propellant. Other active ingredients, such as aluminum salt, emollient, and fragrance, also might seek their own level. By shaking up the can, you would guarantee spraying the proper proportion of ingredients.

Any effort expended in shaking the can is well worth the appreciation from friends and loved ones. But a stiff spray of hydrocarbon gas simply isn't sufficient to take care of a nasty body odor problem.

Submitted by Mark Fusco of Northford, Connecticut.

Why Do Airlines Use Red Carbons on Their Tickets?

The dominant manufacturer of airline tickets is Rand McNally, the same company that makes maps and atlases. We spoke to Chris George, of Rand McNally's Ticket Division, who told us that there are two explanations for the tradition of red carbons.

In the early years of commercial aviation, black carbons were used. This we know for a fact. But Mr. George says the problem with black carbons was that in high humidity specks of black would fall off the ticket. Women, in particular, were upset that their hands or gloves were befouled with black crud. So the airlines did market research that revealed women did not object as much to traces of red on their hands because they were used to rouge and lipstick stains. This, Mr. George adds wryly, is the romantic explanation.

The unromantic explanation (a.k.a. the truth) is as follows: Once your ticket form is torn by the ticket agent, it is sent to the accounting department of the airline. The major carriers have long used optical scanners to read the serial numbers found on each ticket. An OCR (Optical Character Recognition) scanner can't read the ticket when black flecks of carbon land on the serial number because it can only register information printed in black ink. Much as a photocopier will not read blue ink, an OCR scanner won't read red ink. Who would have thought that accountants would be responsible for the daring flash of red on airline tickets?

In a time of high-tech stationery, why don't the airlines use carbonless paper? Part of the answer again relates to the OCR equipment. Carbonless paper contains blue specks that OCRs won't read. Furthermore, with chemically sensitized noncarbon paper, legibility is good for only about five copies. Old-fashioned carbon paper can render nine legible copies, sometimes necessary for the daunting itineraries of business travelers.

Now that most airlines are issuing automated ticket boarding pa.s.ses-the ones that look like computer cards-the decline of the carbonized form is inevitable. Because not all ticket counters possess the equipment to issue these boarding pa.s.ses, Mr. George predicts that the beloved red carbonized forms will continue to play a part in aviation for the foreseeable future.

Submitted by Niel Lynch of Escondido, California.

I Have a Dollar Bill with an Asterisk After the Serial Number: Is It Counterfeit?

The Imponderables staff will gladly accept your dollar bill if you don't want it. No, it's not counterfeit. You are holding a "star note," a replacement for a defective bill that has been destroyed.

In 1910, the Bureau of Engraving and Printing started printing B and later D as prefixes before the serial numbers of replacement notes. No star notes were issued for national bank notes, which were replaced by new notes that matched the missing serial numbers.

Now that notes are issued in series of one hundred million at a time, it is obvious why the Bureau would rather not have to renumber replacement notes, especially since, as Bob Cochran, secretary of the Society of Paper Money Collectors, told us, errors are quite common in the printing process: The most common errors are in inking, cutting, and in the overprinting operation. With inking there can be too much, not enough, or unacceptable smears. Notes are printed in sheets of 32; the back is printed in all green ink and then the face is printed in all black ink. If one side or the other is not registered properly, the designs will not match up on both sides after the sheets are cut up; if the registration is very poor, the notes will be replaced. A third separate printing operation adds the serial number and Treasury Seal; the major error possibilities are in inking and placement, since the basic note design already exists at this point.

You have probably noticed that serial numbers on U.S. currency are preceded by a letter. That letter designates which of the twelve Federal Reserve districts issued the note (this is why the letters span A through L). For example, all serial numbers preceded by D (the fourth letter of the alphabet) are issued by the Fourth District of the Federal Reserve (Cleveland). Here is a list of the twelve Federal Reserve Bank districts and the letter designations for each: District Letter City

1.

A.

Boston

2.

B.

New York

3.

C.

Philadelphia

4.