When Do Fish Sleep? Read Free Page A

register as full, even though the tank can hold more gasoline . The gauge will register full until this “extra” gasoline is consumed and the float starts its descent in the tank. At the other end of the float’s stroke, the gauge will register as empty when the float can no longer move further downward, even though liquid is present below the float .
    We asked Anthony H. Siegel, of Ametek’s U.S. Gauge Division, why sensors aren’t developed that can measure the actual status of gasoline more accurately. We learned, much as we expected, that more precise measurements easily could be produced, but the automakers are using the current technology for our own good:
     
Vehicle makers are very concerned that their customers do not run out of fuel before the gauge reads empty. That could lead to stranded, unhappy motorists, so they compensate in the design of the float/gauge system. Their choice of tolerances and calibration procedures guarantees that slight variations during the manufacturing of these components will always produce a combination of parts which falls on the safe side. The gauge is thus designed to read empty when there is still fuel left.
     
    Tens of millions of motorists have suspected there is fuel left even when the gauge says empty, but few have been brave enough to test the hypothesis. Perhaps there are gallons and gallons of fuel left when the gauge registers empty, and this is all a plot by Stuckey’s and Howard Johnson’s to make us take unnecessary pit stops on interstates.
     
Submitted by Jack Belck of Lansing, Michigan.
     
     

     
     
    How Is the Caloric Value of Food Measured?
     
    Imponderables is on record as doubting the validity of caloric measurements. It defies belief that the caloric value of vegetables such as potato chips and onion rings, full of nutrients, could possibly be higher than greasy tuna fish or eggplant. Still, with an open mind, we sought to track down the answer to this Imponderable.
    Calories are measured by an apparatus called a calorimeter . The piece of food to be measured is placed inside a chamber, sealed, and then ignited and burned. The energy released from the food heats water surrounding the chamber. By weighing the amount of water heated, noting the increase in the water’s temperature and multiplying the two, the energy capacity of the food can be measured. A calorie is nothing more than the measurement of the ability of a particular nutrient to raise the temperature of one gram of water one degree Centigrade. For example, if ten thousand grams of water (the equivalent of ten liters or ten thousand cubic centimeters) surrounding the chamber is 20 degrees Centigrade before combustion and then is measured at 25 degrees after combustion, the difference in temperature (five degrees) is multiplied by the volume of water (ten thousand grams) to arrive at the caloric value (fifty thousand calories of energy).
    If fifty thousand calories sounds like too high a number to describe heating ten liters of water five degrees, your instincts are sound. One calorie is too small a unit of measurement to be of practical use, so the popular press uses “Calories,” really kilocalories, one thousand times as much energy as the lowercase “calorie.”
    The calorimeter is a crude but reasonable model for how our body stores and burns energy sources. The calorimeter slightly overstates the number of calories our body can use from each foodstuff. In the calorimeter, foods burn completely, with only some ashes (containing minerals) left in the chamber. In our body, small portions of food are indigestible, and are excreted before they break down to provide energy. The rules of thumb are that two percent of fat, five percent of carbohydrates, and eight percent of proteins will not be converted to energy by the body.
    Food scientists have long known the caloric count for each food group. One gram of fat contains more than twice the number of calories (nine).
    Scientists can easily