This is the first of two papers concerning an improved transient‐flow method for determining the thermal conductivity and diffusivity of insulating materials in bulk. The work was first suggested by the geophysical problem of determining the thermal constants of natural rock in situ. A cylindrical ``thermal probe,'' containing heat‐source and thermometer, is inserted in the medium and constants deduced from a record of probe temperature versus elapsed time; this method has been used before but the work described here is an attempt to eliminate, or evaluate the effect of, physical idealizations inherent in previous applications. The first paper is concerned with development of a new approximate mathematical treatment, using methods of the operational calculus first suggested by S. Goldstein, in 1932. A subsequent paper will deal with the experimental results obtained with the new theory.

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© 1954 American Institute of Physics.
1954
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