Topic：Why the author mentions that it is impossible to measure the importance of Edison by adding up the specific inventions with which his name is associated?
Because he thinks that although many inventions of Edison have been in their effect upon modem civilization. the total effect of Edison s career surpasses the sum of all of them. He did not merely make the lamp and the photograph and innumerable other devices practicable for general use； it was given to him to demonstrate the power of applied science so concretely， so understandably, so convincingly that he altered the mentality of mankind. In his lifetime，largely because of his successes， there came into widest acceptance the revolutionary conception that man could by the use of his intelligence invent a new mode of living on this planet: the human spirit. which in all previous ages had regarded the conditions of life as essentially unchanging and beyond man's control, confidently and perhaps somewhat naively, adopted the conviction that anything could be changed and everything could be controlled.
