PART 7:  Taking the Heat
 
 
      It rained all through the night.  Inside the tents, the sleepers lay bundled in their sleeping bags.  Protected under the tarp like vestibule of one tent, Puppy was curled up with her tail flopped over her nose for warmth. 
      Mammals like Puppy and her humans maintain their own body temperatures.  Even sleeping, their bodies were busy converting chemical potential energy from their food into thermal energy.  They needed the heat to maintain the chemical reactions that kept them alive.  Blood cells were being replaced.  Muscle tissue was being repaired.  Neurons were rapidly sending messages back and forth as their brains kept a vigil on their vital organs.  Their hearts kept pumping blood through arteries and veins.  Their lungs kept breathing.  Long twisting digestive systems continued to break down the food, removing useless waste and taking energy from the rest. 
      Doing no work on the outside world, the humans used about a hundred watts an hour to do their internal tasks.  Most of the power was used to produce heat.  Maintaining a constant body temperature meant losing thermal energy at the same rate it was produced.  On a cold, rainy night in a tent not losing it too fast was the main concern.  Puppy had a thick coat of fur which trapped warm air near her skin and provided insulation.  Her humans, unfortunately, were not so well endowed.  They did, however, have skin which did not conduct heat very easily, as well as thick layers of skin and fat to help insulate them.  With the air temperature outside dropping to just above the freezing point of water, however, clearly more was needed. 
 
      Big Sister muttered something in her sleep as she tried to curl into a ball inside her constrictive sleeping bag.  Just like Puppy, she was trying to reduce the amount of surface area she had exposed to the air.  Human bodies are awkwardly shaped for this though, and she was not as successful as Puppy.  Her thick sleeping bag provided a good deal of insulation, but she was still losing a lot of heat from her face which was exposed to the cold air in the tent.  Heat leaving her skin warmed a very thin layer of air around her face.  If it could have stayed still, she would have gradually reached an equilibrium with it and not lost more heat.  The air, however, would not stay put.  Outside the tent it was even colder, so near the walls the air grew chilled.  Differences in temperature in different parts of the tent created small convection currents.  The warm air around her face was quickly moved away and replaced by colder air.  As long as her body was warmer than her surroundings heat would continue to leave her.  Father often called this process "trying to single-handedly warm up the Great Outdoors."  Big Sister usually called it things which should not be printed.  
Most of Big Sister's body is well insulated, so she is
primarily losing heat from her face.  The heat moves 
from her warm face to the cold air.  It rises and is cooled
near the walls of the tent. 
 
 
"High tech electromagnetic radiation drier."
       It stopped raining in the morning.  By the time the family had eaten breakfast and cleaned up the cooking area, the sky was beginning to show patches of blue again.  They decided to set their wet clothing out to dry for awhile in the morning sun.  Electromagnetic radiation bombarded the water molecules clinging to the fibers of the cloth and transferred energy to them.  As the water molecules became more energetic, they broke away from the cloth and rose into the air, leaving the now dry clothing behind. 
      "Figures," said Father, glancing up at the dissipating clouds as they took down the tents.  "Now that we're leaving it quits raining.  This weather's not very cooperative." 
      "It's just trying to make sure we have a traditional camping trip," responded Brother.
 
      The tents were stuffed into their bags.  Clothing that had been set out to dry was collected and re-deposited in the packs.  A last minute group photo was taken using the auto timer on Father's camera.  This involved the challenging feat of getting Puppy to stand still while facing the right direction for the picture.  Then the loaded packs were finally hoisted up onto already sore shoulders and the family set off back down the trail. 
      The rain had made the path slimy with mud which had still not dried.  Both Father and Little Sister slipped coming down a small hill when the gravitational force acting on them overcame the meager friction the mud could provide, but no one was hurt.  The air still held the damp chill of nighttime as they started out.  The day was quickly brightening however, and the sun continued to deliver its energy to their skin, warming it quickly.  Soon they had to pause to take off jackets and sweatshirts.
 
      As they hiked, Mother spotted two dall sheep, an eagle, and something gray that moved fast through the distant brushy valley.  Each time she saw something, she pulled out her binoculars to get a better view.  Each half of the binoculars had its own telescope like lens system.  At the front end, light entered through a large objective lens which formed an inverted and reversed image.  The light then entered two prisms.  It entered at such an angle that it did not pass out the other side of the prisms, but instead was internally reflected back.  The first prism reversed the image again and the second flipped the image over to make it right side up.  Bent by the prisms, the path of the light became longer.  This allowed the binoculars to provide a larger magnification by increasing the effective distance between the objective lens and the eyepiece lenses.  Telescopes, which are straight and long, do not need the prisms, but they are also harder to hold steady because of their unwieldy length.  The prism system of the binoculars concentrated the mass all in one easy to hold bundle.  Each of Mother's eyes saw a slightly different image through its side of the binoculars.  Her brain combined the two images into one image with good depth of field. 
      "I think that gray thing was a wolf," she said. 		  
Prism binoculars.  The yellow arrow represents a ray of light.
 
[References used on this page: (Bloomfield, 1997), (Macaulay and Ardley, 1998)]          See bibliography
 
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