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Enclosed in Glass

From the Electric Museum website.

What is an "enclosed" arc lamp? The arc is enclosed by a small oblong inner globe which is almost airtight. After a few minutes of operation the oxygen inside this globe is consumed, thus greatly extending the life of the carbons. These types of lamps could burn for up to about 80 hours on a single set of carbons, whereas earlier "open" designs needed their carbons changed every few hours. Walking along a city street in the early 1900's you never would have guessed that the ornate lamps overhead housed machinery designed to regulate and maintain a superheated plasma arc. Remarkably, this technology was in large scale use by the late 1870's long before the lightbulb was a commercial reality.