Balbo's North Atlantic Flight in 1933 
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Donath lamp

The so-called "Donath lamp" was a portable projector for luminous signals with handle with button for switching on and off the lamp according to the Morse alphabet. Powered by heavy batteries, the lamp was difficult to use especially due to the difficulty encountered in maintaining the direct light beam exactly towards the receiver for the duration of the signal.

From "La centuria Alata" by Italo Balbo:

"At the hydrofoil of the Lido of Rome wait, at my Atlantic apparatus, the other two seaplanes that will be part of the General Staff of the Cruise as helpers and explorers: they are the apparatus of Captain Biseo and Captain This. Both took part to the previous Cruise, in the formation of the current Atlantic Team they will immediately follow the one on the right and the other on the left of my apparatus.I count them to use them for special tasks: for example in the case of fog they can be sent in patrol at different altitudes In case of failure of my radio, I will be able to use them, transmitting to the I-Bise or to the I-Ques the dispatches with the lamp Donath. "