Planting trees to increase rain was the grand climate controversy of the nineteenth century. Some European scientists with diverse backgrounds in physics, meteorology, forests, and soils developed a new science of forest meteorology that blended meteorology, forest ecology, and forest hydrology. They sought answers in direct measurement of forest influences on climate and installed meteorological observatories in forested and open lands to obtain the necessary data. They explained forest influences in the laws of physics, fused with interdisciplinary knowledge of meteorology, forest hydrology, and forest ecology, and gathered the data to further their theories. It was an understanding based on observations of microclimates, but upon which was layered a dynamical framework applicable to macroclimates. Many of the findings have withstood the test of time, and the questions posed are still relevant to today’s scientists.