A remarkable long-lived, large-scale traveling ionospheric disturbance (TID), excited by the May 18, 1980, explosion of Mount St. Helens, has been detected in total electron content monitor data. Oscillatory perturbations in the electron column density of the ionosphere with amplitudes about 10% of the nominal daytime content were detected at three stations whose ionospheric penetration points lie between 1610 and 1890 km from Mount St. Helens. Smaller perturbations were detected at five of six additional stations between 3760 and 4950 km away. The period of the TID increased linearly with great-circle distance from Mount St. Helens, ranging from •37 min at the nearest station to • 116 min at the most distant one. The TID persisted for at least four cycles at the three close stations and three cycles at the more distant stations and was qualitatively similar to TIDs produced by the low-altitude thermonuclear detonations of the 1960's. The disturbance front of this TID accelerated from an average velocity of •350 m/s between Mt. St. Helens and the close stations to an average velocity of •550 m/s to the more distant ones. In analogy with the bomb-excited disturbances, this TID is interpreted as the ionospheric fluctuations induced by a gravity wave, excited by the explosion of Mount St. Helens, propagating in the neutral atmosphere. A model based on the free wave response of an isothermal atmosphere to a point disturbance provides a good fit to the data at the three closest stations, but no such model can account for all of the data. Modeling of the long-distance behavior of the Mount St. Helens TID in terms of upper-atmosphere guided gravity waves is complicated by the requirement of exciting them by a ground-level explosion. A comprehensive explanation would probably include the propagation of energy to ionospheric heights in free modes and the excitation thereby of guided modes. There was no evidence for a strong supersonic shock wave in the ionosphere. As a result, the Mount St. Helens disturbance may prove to be a cleaner test of detailed theories of the point excitation and propagation of gravity waves in a realistic atmosphere than were TIDs excited by thermonuclear weapons.

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Not long ago, the East Bay Municipal Utility District of Oakland, California, faced and solved a stubborn corrosion problem in its large twin‐transmission main. The problem arose originally when the District built its second Mokelumne Aqueduct running parallel with the first for about 83 miles. Shortly after this new line was built, leaks began to appear in the older aqueduct, even though it had been protected by cathodic devices for the previous 15 years. Mr. Hendrickson, who was appointed to solve the problem, states that corrosion in a pipeline is caused by an electric current discharging electrolytically from the pipe to the soil. The source of this electric current may be galvanic or of local action, or it could also be man‐made such as a stray railway current. Mr. Hendrickson's findings are given below from the paper he subsequently gave at the Annual Conference of the National Association of Corrosion Engineers.