Rare autograph letter signed by Charles Darwin's older brother, Erasmus Darwin. Dated 16 December 1851, Erasmus Darwin here writes to the Darwins' legal and financial advisor, Thomas Salt, in part, ''I enclose you the receipt for…Interest up to Dec 15…Eras. Darwin''. Single page on card-style bifolium stationery measures 4.25'' x 7'' as folded. Small hole on last page, else near fine condition.