spores, the theory now known as panspermia. He thought of the idea of a universal language, proposing a modification of the English language. He was a board member for the Swedish Society for Racial Hygiene (founded 1909), which endorsed mendelism at the time, and contributed to the topic of contraceptives around 1910. However, until 1938 information and sale of contraceptives was prohibited in the Kingdom of Sweden. Gordon Stein wrote that Svante Arrhenius was an atheist. In his last years he wrote both textbooks and popular books, trying to emphasize the need for further work on the topics he discussed. In September 1927, he came down with an attack of acute intestinal catarrh and died on 2 October. He was buried in Uppsala. Marriages and family He was married twice, first to his former pupil Sofia Rudbeck (1894–1896), with whom he had one son, , and then to Maria Johansson (1905–1927), with whom he had two daughters and a son. Arrhenius was the grandfather of bacteriologist Agnes Wold, chemist , and ocean biogeochemist . Greenhouse effect In developing a theory to explain the ice ages, Arrhenius, in 1896, was the first to use basic principles of physical chemistry to calculate estimates of the extent to which increases in atmospheric carbon dioxide (CO2) will increase Earth's surface temperature through the greenhouse effect. These calculations led him to conclude that human-caused CO2 emissions, from fossil-fuel burning and other combustion processes, are large enough to cause global warming. This conclusion has been extensively tested, winning a place at the core of modern climate science. Arrhenius, in this work, built upon the prior work of other famous scientists, including Joseph Fourier, John Tyndall and Claude Pouillet. Arrhenius wanted to determine whether greenhouse gases could contribute to the explanation of the temperature variation between glacial and inter-glacial periods. Arrhenius used infrared observations of the moon – by Frank Washington Very and Samuel Pierpont Langley at the Allegheny Observatory in Pittsburgh – to calculate how much of infrared (heat) radiation is captured by CO2 and water (H2O) vapour in Earth's atmosphere. Using 'Stefan's law' (better known as the Stefan–Boltzmann law), he formulated what he referred to as a 'rule'. In its original form, Arrhenius's rule reads as follows: if the quantity of carbonic acid increases in geometric progression, the augmentation of the temperature will increase nearly in arithmetic progression. Here, Arrhenius refers to CO2 as carbonic