e deafness, an excellent listener. No one ever goes
away from Edison in doubt as to what he thinks or means, but he is ever
shy and diffident to a degree if the talk turns on himself rather than
on his work.

If the authors were asked, after having written the foregoing pages,
to explain here the reason for Edison's success, based upon their
observations so far made, they would first answer that he combines with
a vigorous and normal physical structure a mind capable of clear and
logical thinking, and an imagination of unusual activity. But this would
by no means offer a complete explanation. There are many men of
equal bodily and mental vigor who have not achieved a tithe of
his accomplishment. What other factors are there to be taken into
consideration to explain this phenomenon? First, a stolid, almost
phlegmatic, nervous system which takes absolutely no notice of ennui--a
system like that of a Chinese ivory-carver who works day after day and
month after month on a piece of material no larger than your hand. No
better illustration of this characteristic can be found than in the
development of the nickel pocket for the storage battery, an element the
size of a short lead-pencil, on which upward of five years were spent
in experiments, costing over a million dollars, day after day, always
apparently with the same tubes but with small variations carefully
tabulated in the note-books. To an ordinary person the mere sight of
such a tube would have been as distasteful, certainly after a week or
so, as the smell of a quail to a man striving to eat one every day for a
month, near the end of his gastronomic ordeal. But to Edison these small
perforated steel tubes held out as much of a fascination at the end of
five years as when the search was first begun, and every morning found
him as eager to begin the investigation anew as if the battery was an
absolutely novel problem to which his thoughts had just been directed.

Another and second characteristic of Edison's personality contributing
so strongly to his achievements is an intense, not to say courageous,
optimism in which no thought of failure can enter, an optimism born of
self-confidence, and becoming--after forty or fifty years of experience
more and more a sense of certainty in the accomplishment of success. In
the overcoming of difficulties he has the same intellectual pleasure
as the chess-master when confronted with a problem requiring all the
efforts of his skill