The major and most recognised area of Philip's research was his work on the theory of
infiltration. He derived the theory for one dimensional infiltration and developed equations which described the infiltration on both a short term and long term scale, with the revelation that when ponded infiltration in uniform soils occurs, the flow will approach the saturated
hydraulic conductivity: : I = S \sqrt{t}\ + A t where S is
sorptivity and A is the steady-state infiltration rate. Other areas of research include: • Examining heat and mass transfer in soils. • Philip also considered the importance of relationships between organisms and the environment. This included theories on plant canopies, with particular focus on investigation of crop stomatal or surface resistances. Philip was also responsible for the construction of the
Soil plant atmosphere continuum which is used to explain the transfer of water within transpiration paths, a concept which has since been expanded upon. • Philip also studied advection, the horizontal movement of atmospheric properties e.g. temperature and while his analysis and solutions were not completed, his initial work has been important for development of solutions to problems such as long-term flux assessments. ==Achievements==