Signedunsigned
Inscribeda paper label pinned to the base reads: Arc = Tungsten leads / Directions for starting arc: Close short circuit switch on base, tip the lamp slightly on its side and thus connect the two leads with mercury then break the connection. Repeat this until lamp starts. When running for about 30 seconds open the short circuit switch. The lamp draws 3.5 amps aprox. when normal
painted on one side of base: JEFF PHYS LAB / Lecture Room
FunctionThis seems to be an early, experimental discharge lamp that works with mercury vapor. When turned on, it would give a bright, pinkish glow. As the instructions remind us, in order to start these lamps, first the mercury had to be heated by allowing current to pass through it between the electrodes, evaporating some mercury. Only when enough vapor was present would a bright arc extend from one electrode to the other. The coils probably elevate the voltage from the binding posts so that the arc can be formed.
Its instructions imply that it was used for demonstrations, although that does not mean it was its original purpose. It was very probably made at Harvard.
ProvenanceFrom the Department of Physics, Jefferson Physical Laboratory, Harvard University.