MIRROR MIRROR ON THE WALL, WHO'S THE TALLEST OF THEM ALL? 
(Mirror:MT. EVEREST) 
AND JUST HOW TALL IS IT? 
(MIrror:I HAVE NO IDEA.)  
SCIENTISTS DO ACTUALLY USE A MIRROR TO FIND THE HEIGHT OF MT EVEREST, SAYS
GEOLOGIST ROGER BILHAM AT THE UNIVERSITY OF COLORADO.
Bilham:  "There is one there right now, in fact much to the disgust of all the mountaineers, they climb this
mountain and then there's this scientific mirror sitting there as if to say somebody got here before you."
     BUT IT TURNS OUT THAT THE MIRROR ON THE HILL DOESN'T KNOW A LOT MORE
THAN THE MIRROR ON THE WALL.  THE HEIGHT OF MT. EVEREST IS 29,028 FEET GIVE OR
TAKE A FOOT.  THAT SOUNDS GOOD UNTIL YOU REALIZE WE KNOW THE DISTANCE
FROM THE EARTH TO THE MOON TO WITHIN AN INCH.  JUST WHY IS TAKING THE
MEASURE OF A MOUNTAIN SO TOUGH? BILHAM EXPLAINS THAT YOU MEASURE THE
HEIGHT OF MT. EVEREST BY SENDING A LASER BEAM AT THE MIRROR AND MEASURE
THE TIME IT TAKES TO RETURN.  WITH SOME MATH YOU CAN FIGURE OUT THE
DISTANCE BASED ON THAT FLIGHT TIME.  
     Bilham: "The problem is you are assuming that your light is travelling in a straight line, and . . . the
light bends and twists on it's way to the summit depending on the local temperature distribution."
          SCIENTISTS TRY TO CORRECT FOR THESE BENDS IN THE LIGHT BY SENDING UP
BALLOONS TO MEASURE THE AIR TEMPERATURE AT VARIOUS POINTS AROUND THE
MOUNTAIN. 
Bilham:   "to do that accurately you need ten, twenty, maybe a hundred balloons, and of
course the balloon will never exactly follow the path that your beam of light is travelling."
     WE NEED TO FIND ANOTHER MEASURING TECHNIQUE BEFORE WE'RE GOING TO GET
MUCH MORE ACCURATE. SO,  MIRROR MIRROR ON THE HILL, WILL WE EVER KNOW THE
EXACT HEIGHT OF MT. EVEREST?  
(Mirror: ASK AGAIN IN 20 YEARS)