[132] The quantity of air thus separated from water is so great that in the Alps and in the Pyrennees, very powerful bellows are made for forges by the fall of a column of water, through a wooden pipe, into a closed cask, in which it dashes on a stone in the bottom, when the air thus disengaged from it is carried by another pipe placed in the cover of the cask into the foundery. [133] This substance presents with great distinctness those characters which distinguish it from _Hornblende_, viz. inferior hardness, difficult fusibility into a green enamel, and peculiar cleavage which discovers a considerable lustre in one direction which is entirely absent in the other; whereas _Hornblende_ has natural joints of the same lustre in two directions. [134] Mr. Majendie presented some of these specimens to Abbe Haüy, and compared them with those in the cabinet of that illustrious mineralogist, which were brought from the hill of _Mussinet_ near Turin. M. Haüy observed upon this occasion, that the Coverack Specimens did not consist of pure _Diallage_, but that fibres of common _Hornblende_ interrupted its texture. That of _Mussinet_ is foliated, and has no such intermixture. [135] For a long period this was considered as the only Cornish habitat of this mineral; but Dr. Paris subsequently identified its presence in a sand brought from a stream near the house of Colonel Sandys at Lanarth. See "Transactions of the Royal Geological Society of Cornwall." Vol. I. p, 226. [136] See a History of this curious discovery in "A Memoir on the Life and Scientific Labours of the Rev. William Gregor, by J. A. Paris, M. D."--London, 1818. APPENDIX. PART I. A DIALOGUE _Between Dr. A.--a Physician, and Mr. B.--an Invalid, on the comparative merits of different Climates, as places of Winter residence._ "Ne quis _error loci_ nascatur--" _Mr. B._--In a conversation which we held together in the early part of the summer, you will remember the promise you then gave of affording me such advice, relative to the choice of a winter's residence, as the declining state of my health might require. The autumn is now rapidly advancing, and I feel that no time should be lost in making such arrangements as may enable me to pass the approaching winter with the greatest prospect of benefit. _Dr. A._--I fully acquiesce in the propriety of your resolution, and shall readily afford you any information in my power; but you well know that to a physician there is not a question which he approaches with so much diffidence, or dismisses with such little satisfaction.