nose to the trail itself, the dog always goes to one side. The trail smells so strong to the dog that it cannot make the proper distinctions by the trail itself, and cannot tell whether the animal was running one way or the other. It goes to one side and then only it tells by its sense of smell in which direction the scent increases, and so runs after the animal.
It does what we do when any one speaks too loudly in our ear: we move away, and then at a proper distance we distinguish what is said. Or when we are looking at any object which is too near us, we hold it farther from our eyes, and then we look at it.
Dogs recognize one another and communicate with one another by means of smells.
Still more delicate is the sense of smell in insects. The bee flies straight to the flower which it needs. The worm crawls to its leaf. The bug, the flea, the gnat, smell a man distant a hundred thousand times its own length away.
If the atoms emanating from substances and penetrating our nostrils are minute, how infinitesimal must be the particles which affect the smellers of insects!
CHAPTER V
TOUCH AND SIGHT
Twist the index finger with the middle finger and place between these fingers intertwined a small ball in such a way that it touches both, and then shut your eyes. It will seem to you that you are holding two balls. Open your eyes and you will see that it is only one. Your fingers have deceived you, and your eyes have corrected the impression.
Look—best of all a little sidewise—at a good, clear mirror, it will seem to you that it is a window or a door, and that there is something behind it. Touch it with your fingers and you will assure yourself that it is a mirror. Your eyes deceived you, but your fingers corrected the impression.
