Althorp Papers. Vol. mmdccxiii. George Appleyard's catalogue of the books which belonged to William Stephen Poyntz and were inherited by his daughter, Isabella, Marchioness of Exeter; n.d.
Althorp Papers. Vol. mmdcxi. Letters to Lady Mary Elizabeth Ponsonby, wife of Sir Henry Ponsonby, mainly made up of family letters from Charles Robert and Margaret Spencer; 1890-1915, n.d. Sir Henry's grandmother was Henrietta, 3rd Countess Bessborough, daughter of John, 1st Earl Spencer.