Note 3 — ANNO DOMINI 2071.

“Think of the phosphorus discovered by Brandt and Künckel as early as 1669, yet never getting into common use until the lucifers, fusees, and ‘flamers’ made their appearance some two hundred years afterwards; and of chloroform, now the greatest alleviation of suffering humanity, although Dumas, when he first compounded it, did but little dream of its application. Then, again, when Sir Humphry Davy’s remarkable experiments taught him the refrigerating power of metal gas, did this not ultimately lead to the invention of the safety lamp? and not only has the latter already preserved thousands of human lives, but, more than that, the principle of Davy’s invention has actually become the basis upon which all steam-engines are constructed, as well as those by which ice can be made at any time. With regard to the invention of the art of photography, how could it have become a reality, a possibility, without the number of purely scientific discoveries that preceded it; aye, purely scientific discoveries, such as Porta’s so-called camera obscura3 (sixteenth century); Scheele’s discovery of the discoloration of chloride of silver by light, at which he did not arrive until two hundred years afterwards; Courtois’s finding of the iodine, 1811; or the invention of gun cotton, from which Schönbein learned to make collodion; nor would it be difficult to name several other materials, all found by regular chemical processes, to fix the photographic images, and to make them permanent.”