A letter written to President Truman from Albert Einstein discussing his fear of the lack of communication between scientists developing atomic weaponry and those that make policies with it. 

 

http://www.trumanlibrary.org/whistlestop/study_collections/bomb/large/documents/index.php?documentdate=1945-03-25&documentid=3-5&studycollectionid=abomb&pagenumber=1