1. C. H. Henry (private communication).
2. P. M. Morse and H. Feshbach,Methods of Theoretical Physics(McGraw-Hill, New York, 1953).
3. H. S. Carslaw and J. C. Jaeger,Conduction of Heat in Solids(Oxford U.P., New York, 1954).
4. Handbook of Mathematical Functions, Applied Mathematics Ser. 55, edited by M. Abramowitz and I. A. Stegun (National Bureau of Standards, Washington, D.C., 1964).