Unpublished letter, 'Artifically formed diamonds' from James Mactear to the Secretary of the Royal Society Mactear writes: 'as the result of certain speculations on the density of matter, I have been able to produce carbon in the crystalline form, perfectly pure and transparent in colour, and with all the properties of the natural diamond sofar as its power of scratching glass, resisting the action of high degrees of heat, and of acids and alkalis also apparently in its refractive power and crystalline form.' He states that he will communicate the results of his experiments in greater detail. He also shares his observations on the atomic weight of carbon. Subject: Chemistry Received and read 18 December 1879. Written by Mactear in Saint Rollox, Glasgow [Scotland]. 14 December 1879