A letter to the author of the calculations in the White-Hall Evening-Post, relating to South-Sea stock. Shewing the mistakes in the said calculations; and, these being rectified, what the present value of South-Sea stock is. Together with an answer to the unjust insinuations against the estimate of the value of South-Sea stock, lately published, as if that treatise were intended to prejudice the unhappy sufferers who have dealt in South-Sea stock, or to hurt the publick credit. By a member of the House of Commons.