Where could I find the book, A Yankee Adventurer?  And who is the
author?  The book was published in the late 1800s or the early 1900s. 
There was a copy of it in the sterling memorial library at yale in the
1930s.  The story is about Fredrick Townsend Ward's adventures in
China.

Hello  -  thank-you for your question.

The Library of Congress gives these details about the book:

Cahill, Holger, 1887-1960.
Title:         A Yankee adventurer; the story of Ward and the
                  Taiping rebellion, by Holger Cahill.
Published:     New York, The Macaulay Company, 1930.
Description:   7 p. l., 11-296 p. front., illus. (incl. map)
                  plates, ports. 22 cm.
LC Call No.:   DS759.C13
Dewey No.:     923.973 [951] [923.551]
Notes:         Maps on lining-papers.
               Bibliography : p. 295-296.
Subjects:      Ward, Frederick Townsend, 1831-1862.
               China -- History -- Taiping Rebellion,
                  1850-1864.
               China -- History -- Foreign intervention,
                  1857-1861.
Control No.:   5938358

Their catalog is at:

http://catalog.loc.gov/


I was happy to find that there are four first editions of Cahill's
book on offer via Alibris, ranging in price between $31.95 and $74.95,
some in better condition than others.

http://www.alibris.com/search/search.cfm?chunk=25&qtit=A%20Yankee%20Adventurer&qauth=Cahill%2CHolger&qsort=p

The Alibris home page is at:

http://www.alibris.com/

I hope this is helpful - but please feel free to ask for clarification
if necessary.

Regards - Leli