limits of the possible by that faculty known as common sense. And by
common sense is meant, not the appeal to abstract reason, but to
concrete experience.


THE FAILURE OF COMMON SENSE

Common sense had scarce had its laugh at Bell, and its shout of
"I told you so!" at poor Langley, when lo! the telephone became the
world's nervous system, and aeroplanes began to multiply like summer
flies. To common sense the alchemist's dream of transmuting lead
into gold seems preposterous, yet in a hundred laboratories radium
is breaking down into helium, and the new chemistry bids fair to
turn the time-honored jeer at the alchemists completely upside down.
A wife whose mind was oriented in the new direction effectually
silenced her husband's ridicule of what he called her credulity by
reminding him that when wireless telegraphy was first suggested he
had exclaimed, "Ah, that, you know, is one of the things that is not
possible!" He was betrayed by his common sense.

The lessons such things teach us are summed up in the reply of Arago,
the great savant, to the wife of Daguerre. She asked him if he
thought her husband was losing his mind because he was trying to
make permanent the image in a mirror. Arago is said to have answered,
"He who, outside of pure mathematics, says a thing is impossible,
speaks without reason."

Common sense neither leads nor lags, but is ever limited to the
passing moment: the common knowledge of to-day was the mystery and
enchantment of the day before yesterday, and will be the mere