I AM told that I have been the object of severe strictures in your journal for republishing my old “Chemical Physics” as if it were a new book. It is a sufficient answer to say that the book was stereotyped when first issued in 1860, and that there has never been any pretence on my part that it has been revised since. I find, on inquiry, that the American publishers have made, since the first edition, three reprints from the plates, and have called these reprints second, third, and fourth editions, changing, with each issue, the date on the title-page; a usage which I regard myself as reprehensible, but which must be sanctioned by the trade since it is so universally followed. All this time, however, the date accompanying my signature after the preface, and the date of the copyright, have remained unaltered. I had supposed the book entirely out of print; and the last reprint of a very few copies to meet a small demand still existing, chiefly in England, was made entirely without my knowledge or consent. On its very face the whole aspect of the book is antiquated; but in it there was brought together certain positive knowledge in connection with the weighing and measuring of aeriform matter, derived chiefly from the classical researches of Regnault, which is still of great importance and not readily found elsewhere; and this is, unquestionably, the reason of the continued demand for a compilation made more than twenty-five years ago. I have, until within a few years, had the expectation of revising the book and presenting the old facts in their new dress, but the failure of my sight has obliged me to give up the plan, and younger men must do the work.