The north lake in Halemaumau was quite accessible, and we organized night and day shifts for surveying measurements from a canvas shelter on the actual bench lava near the lake. For twenty-minute periods, each observer critically measured a number of monuments on the bench magma and glowing places of the lake edge. Then a new measurement was started by leveling the transit. This sequence was kept up night and day for a lunar month, namely twenty-eight days. One of the monuments was a fixed Halemaumau benchmark, equipped at night with a lantern and used as a datum for the fluctuating lake points. A second tent back from the Halemaumau rim was a camping base. Ford cars were kept running from the Volcano House for the changing of crew, Mrs. Jaggar looked out for the food, and I directed repeated surveys of the position of monuments and of the observation shelter. Meantime the lava steadily rose during July, and at one time split open the Kilauea floor making an outflow back of the shelter. The vertical angles kept track of the movements of both the liquid and the semisolid lava. The instrument was planted on the lava column itself. On one occasion, Mrs. Jaggar’s glove fell into a floor crack inside the shelter and burst into flame. In all, there were more than 20,000 observations recorded. These were plotted on coordinate paper, and results were reduced to a smooth curve by overlapping averages. The actual curve of measurements was subjected to harmonic analysis at Yale University by Professor E. W. Brown, mathematician and specialist on motion of the moon and on lunar tides. The results showed a definite daily tide in both liquid lava and semisolid lava; of a few inches for the lunar tide, and of larger amounts for the solar effect. The curve plotted reached its greatest perfection of daily up-and-down waves during July at periods when the lava was steady. This became interrupted and ragged when accidents of drainage out on Kilauea floor pulled the liquid lava down. [Illustration: _14. River of Alika flow, Mauna Loa, October 6, 1917_] [Illustration: _15. Lava streaming into a sinkhole in Halemaumau lava lake, July 7, 1917_] [Illustration: _16. Sakurajima Volcano, Japan, 1914_] [Illustration: _17. Fountain in lava lake, March 19, 1921_] H. O. Wood, seismologist at the Volcano Observatory, was skilled in compiling the volcano’s historical heights and depths of the nineteenth century and in plotting our curve of surveys of the liquid lava. He published a commentary on such plots for 1912–1913 in relation to solar curves of solstice and equinox, and to the oscillations of the global axis. He demonstrated a definite correlation between seasonal fluctuation of sun and moon and the seasonal rise and fall of the lava, presenting an extensive analysis of the rock tide in the globe and its application to Hawaiian volcanoes for a century. Perret had made a similar analysis for earthquakes and volcanoes in Italy.