14. Crystalline forms of native Diamonds 86 15. Triangular Markings on natural face of a Diamond Crystal 88 16. Triangular Markings artificially produced on a Diamond Crystal 88 17. Diamond-cut Glass and Shavings 98 18. Diamonds in Röntgen Rays. A. Black Diamond in gold frame. B. Pink Delhi Diamond. C. Paste Imitation of B. 98 19. Curve of Vapour Pressure of Carbon _page_ 113 20. Moissan’s Electric Furnace 116 21. Artificial Diamond made by the Author from molten iron 120 22. Moissan’s Artificial Diamonds 120 23. Diamonds from Canyon Diablo Meteorite 138 DIAMONDS CHAPTER I PRELIMINARY From the earliest times the diamond has fascinated mankind. It has been a perennial puzzle--one of the “riddles of the painful earth.” It is recorded in _Sprat’s History of the Royal Society_ (1667) that among the questions sent by order of the Society to Sir Philiberto Vernatti, Resident in Batavia, was one inquiring “Whether Diamonds grow again after three or four years in the same places where they have been digged out?” The answer sent back was, “Never, or at least as the memory of man can attain to.” In a lecture “On Diamonds,” fifty years ago,[1] Professor Maskelyne said, “The diamond is a substance which transcends all others in certain properties to which it is indebted for its usefulness in the arts and its beauty as an ornament. Thus, on the one hand, it is the hardest substance found in nature or fashioned by art. Its reflecting power and refractive energy, on the other hand, exceed those of all other colourless bodies, while it yields to none in the perfection of its pellucidity.” He was constrained to add, “The formation of the diamond is an unsolved problem.”