In 1868 Falb started the popular astronomy magazine, Sirius and began to develop his lunisolar flood theory, published in 1869. A central point of this hypothesis stated earthquakes to be caused by tidal forces acting on subterranean lakes of lava (causing earthquakes) and its upwelling through the earth's crust (causing volcanic eruptions). The strength of these forces being predictable from the positions of the sun and the moon relative to each other, Falb proceeded to postulate Critical Days during which geophysical disasters should be more likely to occur. Subsequently he extended this hypothesis, which initially had strong connections to ideas put forward by the French mathematician Alexis Perrey, to include long-term weather forecasting. Falb's hypothesis gained a high public profile when he made predictions that seemed to come true with the 1873 Belluno earthquake and an eruption at Mount Aetna in 1874.