1. FRICTION. The kindling of machinery, when not sufficiently greased, from the friction of its various parts, has occurred too frequently to require much illustration, although the immediate cause of the phenomenon involves in its consideration so many recondite points in the theory of Caloric, as at present to elude our attempts at explanation; we must therefore rest upon it as an ultimate fact, and be satisfied with availing ourselves of the advantages to which a knowledge of it may conduce. The original inhabitants of the New World, throughout the whole extent from Patagonia to Greenland, procured fire by rubbing pieces of hard and dry wood against each other, until they emitted sparks, or kindled into flame; some of the people to the north of California produced the same effect by inserting a kind of pivot in the hole of a very thick plank, and causing it to revolve with extreme rapidity: this fact will explain how immense forests have been consumed, from the violent friction of the branches against each other by the wind. II. FERMENTATION OF VEGETABLE AND ANIMAL SUBSTANCES. In order to establish the process of fermentation, the presence of water appears indispensable; we accordingly find that in all the cases of spontaneous combustion which have originated from this source, the substances have either been in themselves imbued with moisture, or they have possessed the power of absorbing a considerable portion of water from the atmosphere. The firing of hay, when stacked in too moist a condition, is a striking exemplification of this fact; the same circumstance occurs from great accumulations of turf, flax, and hemp, heaps of linen rags in paper-mills, &c. provided a sufficient portion of moisture be present to excite the process of fermentation, and the consequent evolution of heat. _Oatmeal_, from the extreme avidity with which it imbibes water,[603] and the heat which is generated by the absorption of it, is necessarily liable to spontaneous combustion; the following well authenticated case[604] may serve as an illustration of this fact: “A gentleman removed with his family from Glasgow to Largs, in May last, and shut up his house, which was not re-opened until the end of August; the house stands on the side of a steep declivity, so that the kitchen which is in the back part, though sunk considerably below the level of the street, is entirely above ground, and is well lighted and ventilated. In an opening of the wall, near the kitchen fire-place, originally intended it is supposed for an oven, there was placed a wooden barrel bound with iron hoops, and filled with _oatmeal_. This meal, which had heated during the absence of the family, at last caught fire, and was totally consumed, together with the barrel which contained it, nothing remaining but the iron hoops and a few pieces of charcoal.” In some cases torrefaction increases the propensity of vegetable substances to spontaneous combustion; _coffee_, roasted _French beans_,