The painting was done in Valdemosa, Majorca, where they were spending an autumn.  Sargent's older sister Emily, is in the chair (foreground) reading a book, with their friend Eliza Wedgwood, a member of the famous porcelain manufacturing family, on the sofa (background), either reading or writing a letter. 

Eliza said of it, "Sargent painted in oils such an amusing picture of Emily and me--in what John called 'Garde Mangers,' Emily's invention for keeping out mosquitoes." 

(American Tonalism Detroit Institute of Arts)

Notes:

Bibliography:    

Ormond, Richard, "John Singer Sargent: paintings, drawings, watercolors," New York: Harper & Row, 1970.

Illustration:    

Ormond, Richard, "John Singer Sargent," New York: Harper & Row, 1970, pl. 101.