[7] Sir James Dewar, in a Friday evening discourse at the Royal Institution in 1880, showed an experiment proving that the temperature of the interior of a carbon tube heated by an outside electric arc was higher than that of the oxy-hydrogen flame. He placed a few small crystals of diamond in the carbon tube, and, maintaining a current of hydrogen to prevent oxidation, raised the temperature of the tube in an electric furnace to that of the arc. In a few minutes the diamond was transformed into graphite. At first sight this would seem to show that diamond cannot be formed at temperatures above that of the arc. It is probable, however, for reasons given above, that at exceedingly high pressures the result would be different. [8] The silica was in the form of spheres, perfectly shaped and transparent, mostly colourless, but among them several of a ruby colour. When 5 per cent of silica was added to cordite, the residue of the closed vessel explosion contained a much larger quantity of these spheres. [9] A pressure of fifteen tons on the square inch would exist not many miles beneath the surface of the earth. [10] There are abundant signs that a considerable portion of this part of Africa was once under water, and a fresh-water shell has been found in apparently undisturbed blue ground at Kimberley. [11] The water sunk in wells close to the Kimberley mine is sometimes impregnated with paraffin, and Sir H. Roscoe extracted a solid hydrocarbon from the “blue ground.” [12] _Chemical News_, vol. lxi, p. 209, 1890. TRANSCRIBER’S NOTE Obvious typographical errors and punctuation errors have been corrected after careful comparison with other occurrences within the text and consultation of external sources. All misspellings in the text, and inconsistent or archaic usage, have been retained: for example, unfrequent; clayey; friable; slaty; imbed; stoped; peculation; situate. In the Table of Contents, the Index page number ‘145’ has been replaced by ‘141’. In the Index, ‘Colesberg Copje’ has been replaced by ‘Colesberg Kopje’, and ‘DeBeers’ has been replaced by ‘De Beers’. End of the Project Gutenberg EBook of Diamonds, by William Crookes