TLamppost he Living
Come, we are going to visit a small Jewish village in rural Russia. Hop into the time machine, and back we travel to the last century.
arily, you step out of the machine and look around. The short winter day draws to a close, and the early dusk envelops the brown street with its huddled low-built wooden houses. Nighttime falls, and the whole village descends into darkness. Here and there a pool of light from an oil lamp spills into the street, but otherwise, there is not a glimmer. Gingerly you walk, not knowing where you are going, your feet slipping and unsure in the grooved path. As night deepens, the blackness intensifies, and you wonder how the inhabitants manage to get about. The answer is that they don’t. The blackness of the night imprisons everyone in their homes. Not a gas lamp, not a glimmer or a spark to break the barrier of blackness. Suddenly you feel a great wave of yearning – a longing to be back in a society which is illuminated and bright, where electricity brightens your night and guarantees your freedom of movement. It’s time to come back to today, to the age of brightness. What could be more modern than streetlamps? If you can remember the lamplighter who went around with his ladder to “windup” the gas lamps, tell nobody your age! Today, no one winds up, no one sets a time switch, and no one pours in the oil. At dusk and dawn, millions of street lights turn themselves on and off with no human intervention at all. Do you know how it works? With a pecu! “Pecu” is the acronym for a photo electric control unit, which operates a switch in the electrical supply to the lights. There, up above, on the street lamp, lies a photocell. The photocell contains a compound (cadmium sulphide or silicon) which is sensitive to light. As dawn rises, light falling on the photocell causes electrons to flow from one atom to the other, conducting electricity to the 22
switch and turning it off. At the other end of the day, as darkness falls, the electrons in the compound become immobile, the current stops, and the lights are turned on. Brilliant! No matter how early darkness falls, the lights will faithfully switch on, thanks to the advanced technology of our modern times. As far as street lighting is concerned, the “good old days” were not so good. Shh! I hear someone laughing. Shh! I hear it again. Who is it? A leaf! Why are you laughing, what are you saying? I don’t believe it! The leaf is saying that its technology is so complex that it makes our most modern street lamps appear primitive in comparison. Could you explain?
The Trees’ Bedtime The autumn season is often called “fall,” and the reason is obvious. When the days become shorter and the temperature begins to drop, millions of trees shed their leaves. The falling of the leaves of the deciduous trees (trees that lose their leaves in autumn, forming new ones in spring) gives the season its distinctive name. It is a spectacular process. The leaves of these trees turn a brilliant red and gold, providing a festival of color which has become a major tourist attraction in many parts of America. Beautiful it certainly is. But what makes the leaves fall from the tree? How is it that the twigs do not descend with the leaves? And why don’t evergreen trees see the need to drop their leaves like other trees do? And then we come to the most enigmatic question of all. How do the trees know when it is time to dispense with their leaves? What is the timing device, the pecu, that triggers the mechanism and starts the process? Prepare to hear some answers that will amaze you.