Few of us, I think, give much thought to the marvelous piece of mechanism that is a dog’s nose. Let’s compare it with a manmade device that has nothing to do with the sense of smell, but is a fair sample of scientific accuracy as applied to modern mechanics.
I’ve read that at one of the big steel plants they impress important visitors by drilling a small hole in a oneton block of steel and tooling a little bar of the same metal to fit it. Both processes are done with such accuracy that, while the bar easily slips in and out of the hole, when it is inserted the naked eye cannot detect where the block ends and the bar begins. Then comes the dramatic moment. The bar is removed from the block, the temperature of the block raised ten degrees, and the bar will no longer enter the hole. The infinitesimal expansion of the block prevents it. Mechanical accuracy plus.
Now what has the nose of an ordinary everyday hound to offer in the accuracy line? At one o’clock some frosty fall morning a fox trots along a brushy hillside hoping to pick up an unsuspecting rabbit. Five hours later a hound strikes his trail. What happens? If scenting conditions are poor the dog may follow the trail in the wrong direction for a hundred yards or even more before he decides he’s backtracking and goes into reverse. If scenting conditions are good it will require only a hundred feet, or in some cases only fifteen or twenty, to get him going right. But we’ll call it a hundred.
The fox covered that distance in about ten seconds. Which means the hound’s nose was so incredibly sensitive it detected a difference of ten seconds in age between two sets of footprints made five hours before. Compared to that brand of black magic the steel block and bar were as crude as a tencent tape measure.