1. Statens Vaginstitut, Med.;Beskow,1935
2. Temperatura do terreno;de Morais;Memorias e Noticias,1955
3. Account of some experiments on the temperature of the Earth at different depths, and in different soils, near Edinburgh;Forbes;Trans., R. Soc. Edinburgh,1846
4. Underground temperatures at Colombo Observatory;Kandasamy;Ceylon J. Science,1937
5. Proj. Paper;Leffingwell,1919