When Do Fish Sleep? Read Free Page B

ascertain the proportion of fat to carbohydrates or proteins, so it might seem that calories could be measured simply by weighing the food. When a food consists exclusively of proteins and carbohydrates, for example, one could simply multiply the weight of the food by four to discover the calorie count.
    But complications arise. Certain ingredients in natural or processed foods contain no caloric value whatsoever, such as water, fiber, and minerals. Foods that contain a mixture, say, of water (zero calories), fiber (zero calories), proteins (four calories per gram), fats (nine calories per gram), and carbohydrates (four calories per gram), along with some trace minerals (zero calories), are simply harder to calculate with a scale than a calorimeter.
     
Submitted by Jill Palmer of Leverett, Massachusetts .
     
     

     
     
    Who Put E on Top of the Eye Chart? And Why?
     
    Professor Hermann Snellen, a Dutch professor of ophthalmology, put the E on top of the eye chart in 1862. Although his very first chart was headed by an A, Snellen quickly composed another chart with E on top.
    Snellen succeeded Dr. Frans Cornelis Donders as the director of the Netherlands Hospital for Eye Patients. Donders was then the world’s foremost authority on geometric optics. Snellen was trying to standardize a test to diagnose visual acuity, to measure how small an image an eye can accept while still detecting the detail of that image. Dr. Donders’ complicated formulas were based on three parallel lines; of all the letters of the alphabet, the capital E most closely resembled the lines that Dr. Donders had studied so intensively. Because Donders had earlier determined how the eye perceives the E, Snellen based much of his mathematical work on the fifth letter.
    The three horizontal limbs of the E are separated by an equal amount of white space. In Snellen’s original chart, there was a one-to-one ratio between the height and width of the letters, and the gaps and bars were all the same length (in some modern eye charts, the middle bar is shorter).
    Louanne Gould, of Cambridge Instruments, says that the E, unlike more open letters like L or U, forces the observer to distinguish between white and black, an important consitituent of good vision. Without this ability, E’s begin to like B’s, F’s, P’s or many other letters.
    Of course, Snellen couldn’t make an eye chart full of only E’s, or else all his patients would have 20-10 vision. But Snellen realized that it was important to use the same letters many times on the eye charts, to insure that the failure of an observer to identify a letter was based on a visual problem rather than the relative difficulty of a set of letters. Ian Bailey, professor of optometry and director of the Low Vision Clinic at the University of California at Berkeley, says that it isn’t so important whether an eye chart uses the easiest or most difficult letters. Most eye charts incorporate only ten different letters, ones that have the smallest range of difficulty.
    Today, many eye charts do not start with an E—and there is no technical reason why they have to—but most still do. Dr. Stephen C. Miller, of the American Optometric Association, suggests that the desire of optical companies to have a standardized approach to the production of eye charts probably accounts for the preponderance of E charts. And we’re happy about it. It’s a nice feeling to know that even if our vision is failing us miserably, we’ll always get the top row right.
     
Submitted by Merry Phillips of Menlo Park, California.
     
     
    Do the Police Really Make Chalk Outlines of Murder Victims at the Scene of the Crime? Why Do They Use Chalk?
     
    As soon as law enforcement officials descend upon a murder scene, a police photographer takes pictures of the corpse, making certain that the deceased’s position is established by the photographs. The medical examiner usually wants the body as soon as possible after the murder; the