Frank P. Fritchle, "Fitch's Apparatus for the Measurement of The Thermal Conductivity", AJP, Vol. 19, #8, Nov. 1951, p. 475.
Robert Ehrlich, "I.8. Measuring Thermal Conductivity from Rate of Heat Loss", Turning the World Inside Out and 174 Other Simple Physics Demonstrations, p. 120 - 121.