S. Q. C. Lamar to General Humphrey, February 2, 1876

S. V. Benet to Thomas Lincoln Casey, December 1870

S. V. Benet to Thomas Lincoln Casey, June 1871

Sadie Gould to Thomas Lincoln Casey, September 2, 1882

Sadie L. Gould to Thomas Lincoln Casey, February 1, 1882

Sam Randall to Thomas Lincoln Casey, April 12, 1875 (1)

Sam Randall to Thomas Lincoln Casey, April 12, 1875 (2)

Sam Randall to Thomas Lincoln Casey, February 8, 1889

Samuel C. Cobb to Thomas Lincoln Casey, February 22, 1882

Samuel C. Cobb to Thomas Lincoln Casey, February 24, 1882

Samuel C. Cobb to Thomas Lincoln Casey. February 20, 1882

Samuel M. Matson to Thomas Lincoln Casey, May 17, 1856

Samuel Pierce Clark to Thomas Lincoln Casey, January 4, 1856

Samuel Ward Green to Thomas Lincoln Caseye, May 21, 1895

Samuel Ward Greene to Thomas Lincoln Casey, August 18, 1882

Sarah Burlingame Webster to Thomas Lincoln Casey, June 15, 1895

Sarah Burlingame Webster to Thomas Lincoln Casey, June 26, 1895

Sarah N. Barnswell, undated [1882]

Sarah N. Randolph to Thomas Lincoln Casey, May 12, 1882, telegram

Sidney S. Rider to Thomas Lincoln Casey, January 6, 1892

Sidney S. Rider to Thomas Lincoln Casey, July 27, 1894

Sidney S. Rider to Thomas Lincoln Casey, June 21, 1881

Sidney S. Rider to Thomas Lincoln Casey, June 27, 1894

Sidney S. Rider to Thomas Lincoln Casey, May 13, 1893

Sidney S. Rider to Thomas Lincoln Casey, November 12, 1894

Sidney S. Rider to Thomas Lincoln Casey, November 30, 1878

Sidney S. Rider to Thomas Lincoln Casey, October 12, 1886

Silas Casey to Thomas Lincoln Casey, April 8, 1892

Silas Casey to Thomas Lincoln Casey, January 26, 1892

Silas Casey to Thomas Lincoln Casey, March 12, 1892

Simeon Draper to Thomas Lincoln Casey, September 2, 1856

Simeon Draper to Thomas Lincoln Casey, September 9, 1856

Simon Newcomb to Thomas Lincoln Casey, November 15, 1880

Society of River and Harbor Engineers - Circular, Constitution and By-Laws, October 5, 1882

Society of the Army of the Potomac to Thomas Lincoln Casey, May 15, 1893

Sophia G. Casey to Thomas Lincoln Casey, June 5, 1881

Sophia G. Casey to Thomas Lincoln Casey, May 28, 1872

Sophia G. Casey to Thomas Lincoln Casey, May 29, 1872

Sophie G. Casey to Thomas Lincoln Casey, May 3, 1872

Spaulding to Thomas Lincoln Casey, February 25, 1870

Specific Gravity of Marble, April 4, 1883

Specifications for bidders for Torpedoes, May 1889

Specifications of Electric Lighting, undated

Speech of Hon. Henry W. Slocum to Thomas Lincoln Casey, February 14, 1871

Spencer F. Baird to Thomas Lincoln Casey, March 31, 1882

Spirito Bernardi to Louisa Seymour, February 24, 1892

Spoffard to Thomas Lincoln Casey, November 15, 1895

St Paul & Duluth R. R. Co. to Thomas Lincoln Casey, June 25, 1889

St. John's Rectory to Thomas Lincoln Casey, January 5, 1892

Stability of the Foundations of the Washington Monument, undated