[98] In February 1812, he exhibited a model, in one of his lectures at the Royal Institution, in illustration of his plan; from which it appeared that the air deteriorated by respiration was conducted through three copper pipes, terminating in a single tube, to the roof of the building; and by means of ventilators below, there was a constant supply of fresh air, the circulation of which was promoted by a furnace.
[99] "Elements of Chemical Philosophy," to be presently noticed.
[100] Specimens of substances ejected from the crater in that island, which Mr. Clayfield forwarded to Davy, in consequence of having heard that he had been engaged in examining the sand collected at Barbadoes, and which was a product of the same eruption.
[102] Iodine, Fluorine, &c. had not been discovered at this period.
[104] See his Salmonia, Edit. 2. p. 9.
[105] Edinburgh Review, vol. 22, page 253.
[106] For example:—What weight of wheat is equivalent to a given weight of oats, barley, rye, &c.? Suppose three hundred pounds of potatoes feed twenty head of cattle for any given time, how many will the same weight of oats feed?
[107] The history of his native county would have furnished him with a parallel instance of the intelligence and design which Nature displays in connecting the wants and necessities of the different parts of creation, with the power and means of supplying them. In a primitive country like Cornwall, the siliceous soil necessarily requires much moisture, and we may perceive that the cause which occasions, at the same time supplies this want; for the rocks elevated above the surface, solicit a tribute from every passing cloud; while in alluvial and flat districts, where the soil is rich, deep, and retentive of moisture, the clouds float undisturbed over the plains, and the country frequently enjoys that uninterrupted series of dry weather which is so necessary to its fertility. Linnæus observes, that the plants which chiefly grow upon the summit of mountains, are rarely found in any other situation, except in marshes, because the clouds arrested in their progress by such elevations, keep the air in a state of perpetual moisture.