[A] The passages marked with inverted commas in praise of what Sir N. H. Nicolas now condemns, are, _mutatis mutandis_, from his own letter of the 20th of October, 1837, inserted above, p. 5. They were not so marked in my original letter of the 25th of May. Sir Nicholas complains of this in the following words: "The English Public would learn with astonishment, the manner in which, by a series of _unmarked_ quotations, a generous letter may be perverted to ungenerous purposes." The purpose for which I used his letter, was my own defence against his attacks,--his own former words being the most triumphant answer to his _recent_ opinions; and I do not see why I should be found fault with, because I have shown that Sir Nicholas unsays _now_ what he has formerly said, though he denied having said it. Does he mean to avow at last, that he has ventured to attack me _recently_, because he had forgotten, _not_ his former opinions, (opinions so strongly entertained are _not_ forgotten) but his having expressed them? A. P. [B] It seems--from the impression which others have of this occurrence which I have totally forgotten,--that Sir N. H. Nicolas could not obtain the Index, because it was not entered in the Catalogue; whence I concluded that it was not in the Library. If all this be true, it only proves _an error in the Catalogue_; but it has nothing to do with the working of the system, as Sir N. H. Nicolas must know as well as I do. A. P. [C] This letter has been inserted above, page 7. * * * * * TRANSCRIBER'S NOTES: Text in italics is surrounded with underscores: _italics_. Inconsistencies in spelling and hyphenation have been retained from the original. Punctuation errors have been corrected without note. Superscripted characters are indicated by a carat character with the superscripted characters in curly braces: 8^{o}.