Sydna Eldridge (1846 - 1936) was a hydrographer and publisher of nautical charts active in the mid-1920s, a member of the family of George Eldridge, a noted hydrographer of the late 19th and early 20th century. When George Eldridge died in 1900, the firm passed to his son George Washington Eldridge (d. 1914). Sydna has been noted elsewhere as George Washington Eldridge's granddaughter, born to his daughter and son-in-law Wildred O. White, but U.S. Census records indicate that she was in fact George Washington Eldridge's wife. In any event, in 1914, when George Washington Eldridge died, the firm came to be managed by Wildred O White. For a period in the late 1910s to the mid-1920s, the firm published charts copyrighted to Synda Eldridge but with White listed as publisher, until the last Eldridge charts were published in 1924. However, White's son and descendants have continued to publish annual editions of Eldridge tide and pilot book down to the present.