We afterwards visited the bomb craters in the source region, to find that there had been numerous hits on the lava tunnel and that the cooling off had solidified the source lava back into the mountain rift. The remainder of the eruption expended itself with internal fountaining in the summit wells at the top end of the flank rift. From the coincidence of the times of bombing and the slowing down of frontal flow, there appeared no question that the smashing of the source tunnel was effective and had saved Hilo. We had not anticipated that active fountaining would be forced back to the summit well from the 9,000-foot craterlet, but summit smoke continuing for two months verified that this had happened. This showed the physical chemistry of bubbling slag to be in delicate adjustment and a lava eruption once started to be more sensitive to shock than anyone had dreamed. This conclusion was reconfirmed by the bombing of the 1942 flow. During this period, changes in Observatory personnel led to new researches. Wingate, who succeeded Wilson as engineer, set up triangulation monuments in Puna to test further motion on the Kapoho rift of 1924. He also devised and set up three tilt instruments in three cellars which were blasted out of the lava around Halemaumau pit. Howard Powers came from Harvard as petrologist and collected and mapped many rock specimens in Kona, on Hualalai, and in Olaa. He also made curves of the tilt records for the first twenty years of the Observatory. Hugh Waesche was transferred from the Park Service to the position of geologist at the Observatory. A skilled radio amateur, he took over seismological work. In 1938 he dealt with an important group of earthquakes along the Chain of Craters east of Kilauea. These were accompanied by faulting, which made cracks, chasms, and humps in the road, and some new hot places. This indicated a reaction underground, back toward Halemaumau from the submarine outflow of April 1924. Finch from his headquarters at Lassen reported regularly in the _Volcano Letter_, on hot spring temperatures and earthquakes. He conducted two expeditions to Alaska, inspecting the seismographs and making volcano explorations and maps on Akutan Island. Another expedition was to Shishaldin Volcano, at the west end of the big Aleutian island of Unimak during one of its eruptive spells. Throughout this time and earlier H. T. Stearns represented the Geological Survey and the Territory of Hawaii in publications on geology and water supply on all the islands. The island of Hawaii was made the subject of a splendid geological map in color by Stearns and Gordon Macdonald, petrographer, with a book on the geological history of Hawaii, profusely illustrated with photographs and diagrams. Their book is practically a modern textbook on the geology of active lava volcanoes.