April 16, 1965

Dr. S. H. Eisman

SMUFA - 1312 (L6200)

Frankford Arsenal

Philadelphia, Pennsylvania 19137

Dear Dr. Eisman:

Professor Polya has called my attention to the paper by Jordan which discusses
both kinds of center of a tree. My discussions, following Henze and Blair,
have concerned his "center" (p. 187), which can be thought of as a center of
mass, and your remarks called attention to his "centre de seconde espece"

(p. 189), which divides the diameter. He also anticipates the mapping of
linear chains on single edges of a graph.

As for the utility of the diameter, I could not improve on your appraisal. It
conforms more closely to conventional nomenclature, but would be very difficult
to manipulate to find all the isomers of a given mass. It might play a useful
role in finding all the homologues derived from a skeleton with a given diameter.

VoMslZ

Sincerely yours,

Joshua Lederberg
Professor of Genetics

Reference: Jordan, C. (1869). Sur les assemblages des lignes.
J. rein. angew. Math., 70:185-190.