 If both wicks are lit, a common, broad flame (zungenfoermige Flamme) results.It is also mentioned in the novels and "Berlin" by Theodore Plievier, as used on the Eastern Front and in air raid shelters respectively.Also it is mentioned in "Wheels of Terror" by Sven Hassel and "In Deadly Combat A German Soldier's Memoir of the Eastern Front" by Gottlob Herbert Biedermann.