d in or upon the metal), and
increase the infusibility of the platinum, led him to aim at securing
greater perfection in the vacuum, on the theory that the higher the
vacuum obtained, the higher would be the infusibility of the platinum
burner. And this fact also was of the greatest importance in making
successful the final use of carbon, because without the subjection of
the carbon to the heating effect of current during the formation of the
vacuum, the presence of occluded gases would have been a fatal obstacle.

Continuing these experiments with most fervent zeal, taking no account
of the passage of time, with an utter disregard for meals, and but
scanty hours of sleep snatched reluctantly at odd periods of the day
or night, Edison kept his laboratory going without cessation. A great
variety of lamps was made of the platinum-iridium type, mostly with
thermal devices to regulate the temperature of the burner and prevent
its being melted by an excess of current. The study of apparatus for
obtaining more perfect vacua was unceasingly carried on, for Edison
realized that in this there lay a potent factor of ultimate success.
About August he had obtained a pump that would produce a vacuum up to
about the one-hundred-thousandth part of an atmosphere, and some time
during the next month, or beginning of October, had obtained one that
would produce a vacuum up to the one-millionth part of an atmosphere.
It must be remembered that the conditions necessary for MAINTAINING this
high vacuum were only made possible by his invention of the one-piece
all-glass globe, in which all the joints were hermetically sealed during
its manufacture into a lamp, whereby a high vacuum could be retained
continuously for any length of time.

In obtaining this perfection of vacuum apparatus, Edison realized that
he was approaching much nearer to a solution of the problem. In his
experiments with the platinum-iridium lamps, he had been working all
the time toward the proposition of high resistance and small radiating
surface, until he had made a lamp having thirty feet of fine platinum
wire wound upon a small bobbin of infusible material; but the desired
economy, simplicity, and durability were not obtained in this manner,
although at all times the burner was maintained at a critically high
temperature. After attaining a high degree of perfection with these
lamps, he recognized their impracticable character, and his mind
reverted to the opinion he