“My son, for whom you express a friendship, and which he warmly returns, encourages me to think that it may not be disagreeable to you to give me information occasionally of what is passing in the philosophical world, now that I am at so great a distance from it, and interested, as you may suppose, in what passes in it. Indeed, I shall take it as a great favour. But you must not expect anything in return. I am here perfectly insulated, and this country furnishes but few fellow-labourers, and these are so scattered, that we can have but little communication with each other, and they are equally in want of information with myself. Unfortunately, too, correspondence with England is very slow and uncertain, and with France we have not as yet any intercourse at all, tho we hope to have it soon.... “I thank you for the favourable mention you so frequently make of my experiments, and have only to remark that in Mr. Nicholson’s Journal you say that the conducting power of charcoal was first observed by those who made experiments on the pile of Volta; whereas it was one of the earliest that I made, and gave an account of in my History of Electricity, and in the Philosophical Transactions. And in your treatise on the Nitrous Oxide p. 55 you say, and justly, that I concluded this air to be lighter than that of the atmosphere. This, however, was an error in the printing that I cannot account for. It should have been _alkaline air_, as you will see the experiment necessarily requires. “With the greatest esteem, I am Sir, yours sincerely “J. PRIESTLEY.” In Davy’s next contribution, “On the Silex composing the Epidermis, or External Bark, and contained in other parts of certain Vegetables,” published in Nicholson’s Journal in the early part of 1800, we find the evidence of a chastened and contrite spirit. The theme is humble enough, and the language as sober and sedate as that of Mr. Cavendish. The chance observation of a child that two bonnet-canes rubbed together in the dark produced a luminous appearance, led him to investigate the cause, which he found to reside in the crystallised silica present in the epidermis. Reeds and grasses, and the straw of cereals, were also found to be rich in silica, from which he concludes that “the flint entering into the composition of these hollow vegetables may be considered as analogous to the bones of animals; it gives to them stability and form, and by being situated in the epidermis more effectively preserves their vessels from external injury.” It is doubtful, however, whether the rigidity of the stems of cereals is wholly due to the silica they contain.