Brilliant_ The Evolution of Artificial Light - Jane Brox [47]
As the New York Herald reported, work there went on all through the night:
At six o'clock in the evening the machinists and electricians assemble in the laboratory. Edison is already present, attired in a suit of blue flannel, with hair uncombed and straggling over his eyes, a silk handkerchief around his neck, his hands and face somewhat begrimed.... The hum of machinery drowns all other sounds and each man is at his particular post. Some are drawing out curiously shaped wires so delicate that it would seem an unwary touch would demolish them. Others are vigorously filing on queer looking pieces of brass; others are adjusting little globular shaped contrivances before them. Every man seems to be engaged at something different from that occupying the attention of his fellow workman.
Edison focused a good deal of attention on the search for the best material for the filament, having concluded that the filament for the bulb had to be constructed of high-resistance material. "The more resistance your lamp offers to the passage of the current," he explained, "the more light you can obtain with a given current." In the course of many months, his crew tried and abandoned materials—carbon, platinum, silicon, boron—and then returned to carbon, which offered high resistance, although it was difficult to stabilize. They carbonized fishing line, rosewood, hickory, spruce, coconut fibers, and countless other substances. They shaped filaments as boxes, spirals, circles, horseshoes, and fanciful sprouts and curlicues, recording every experiment in a series of notebooks. To glance at even a few of the entries is to begin to comprehend the breadth and detail of their attempts:
(April 29) Wood loop cut from the thin worked holly milled by Force and cut after manner and in same former used for cardboard, carbonized by Van Cleve, were measured and put in lamps ready for pump, resistance 125 and 194 ohms.
(May 14) Carbonization. Several moulds of Bast fibers were carefully prepared and formed around wood for carbonization, but the wood proved very detrimental, every one having been broken in the moulds during the process. Van Cleve is preparing some more for trial.
(May 20) Carbonization. Van Cleve carbonized three moulds of bent wooden loops by securing the strips in slotted nickel plates; he got them out very nicely and in good shape. Bast fiber. Four of the Bast fiber lamps were measured and tested with current of 103 volts[;]they gave 30 to 32 candles and about six per horse power. They were connected to main wires in Laboratory and during the first hours three of them broke in the clamps and glass but the fiber in each instance remained in the globe unbroken. Showing the fiber to make strong carbon but difficult to form good contact with.
On October 22, 1879, Charles Batchelor, Edison's most trusted associate, placed a horseshoe-shaped filament of carbonized cotton thread in an evacuated handblown glass bulb and attached it to a series of batteries. The bulb began to glow at 1:30 A.M. and glowed through the rest of the night and the following morning. At 3:00 in the afternoon, he added more battery cells for additional power, and Batchelor noted that the bulb became as bright as three gas jets of the time, or four kerosene lamps: the brilliance of about thirty candles. An hour later, in the waning of a late-fall afternoon, the glass bulb cracked. It had burned for more than fourteen hours.
Everyone working at Menlo Park knew that all aspects of the system needed further improvement before the light would be commercially viable—the dynamo, the switches, the bulb, and the filament, for which they would eventually turn to bamboo. Still, by December Edison was able to display his system to his financial backers. At the same time,