SOME of the problems that have to be solved when protecting airships against fire, due to electric sparks in the neighbourhood of free hydrogen, are discussed in an article in The Times of October 18. The latest German airship, the LZ 130, which inherits the name of Graf Zeppelin, is denied the use of helium, and so uses hydrogen gas. Dr. Hugo Eckener and his colleagues are engaged in experiments during flight to test a project for making the potential of the static electricity within the airship frame equal to that of the electrical field outside. The experiments are based on the use of a new instrument which records the nature and intensity of the static charge in the airship and of the electrical conditions in the atmosphere surrounding the hull. Its function appears to be that of warning the captain of conditions in which it would be dangerous to Valve' gas or to have an appreciable leak of gas. There is little danger even when the aircraft passes through a field of opposite charge, unless there is a gap in the bonded structure across which a spark may jump. If the new instrument works satisfactorily, it would give a warning when the conditions were dangerous and special precautions could be taken. It would enable the captain to see whether or not it was desirable to earth a positive charge when in the neighbourhood of a negatively charged cloud. Such stations have been made in miniature and experiments on a small scale have been carried out. Experiments will shortly be made in full scale under natural conditions.