The engineer was asked if there was any suggestion of the structure adopted by him in the books on engineering. “No,” he said, “it came to me in this way. I was driving by the place where the first attempts were made, of which a colony of bank-swallows had taken possession. It occurred to me that these little engineers had disproved the assertion that this material had no cohesion. They have their homes in it, where they raise two families every summer. Every home is a tunnel, self-sustaining without masonry. A larger tunnel can be constructed by simply extending the principle, and adopting masonry. This is the whole story. The bank-swallow is the inventor of this form of tunnel construction. I am simply a copyist--his imitator.” CHAPTER XXI EXPERIMENT Newton, Watt, Ericsson, Rowland, as boys were constructive . . . The passion for making new things . . . Aid from imagination and trained dexterity . . . Edison tells how he invented the phonograph . . . Telephonic messages record themselves on a steel wire . . . Handwriting transmitted by electricity . . . How machines imitate hands . . . Originality in attack. Early Talent in Construction. An inventor is a man of unusual powers. To begin with he is cast in a larger mold than ordinary men; he has keener eyes, more skilful hands, a better knitting quality of brain. In his heart he believes every engine, machine, and process to be improvable without limit. He is thoroughly dissatisfied with things as they are and alert to detect where an old method can be bettered, or a gift wholly new be conferred on mankind, as in the telephone or the phonograph. His uncommon faculty of observation we have had occasion to remark. Another talent as much in evidence, and quite irrepressible even in early life, impels him to make, weave, and build. Invariably the man who has added to the resources of architecture, engineering, machine design, has begun as a boy in repeating the rabbit-hutches, windmills, and whittled sailing craft of bigger boys. This means that he soon acquires a mastery of chisel, plane, and drill, that the lathe becomes as obedient to him as his own hand. Watt, Maudslay, Stephenson, and every peer they ever had, could go to the bench and make a valve, a mitre-wheel, a link-motion just as imaged in their mind’s eye. Lacking this dexterity other men, occasionally fertile in good ideas, never bring them to the birth.