Then appeared upon the scene the famous Lavoisier, he to whom the Convention refused a fortnight's reprieve from the guillotine, just as he was on the threshold of a probably sublime discovery in the science of light; Fouquier-Tinville returning him for answer that the Republic had no need of chemists and _savants_. In the presence of Lavoisier, Maillard, another jeweller, took three diamonds and closely packed them in powdered charcoal in an earthen pipe-bowl in a strong fire; and when the pot was taken out, there lay the diamonds in the powdered charcoal untouched. It was, however, gradually discovered that it was only by entirely shutting out the air, and therefore the oxygen with which the carbon combines, that the diamonds were preserved from burning; whereas by the simple admission of air, of which oxygen is a constituent part, diamonds burn just the same as common coal. This was proved by Lavoisier in 1776; and Davy subsequently shewed that the diamond contains no hydrogen. So, when the most precious object which the earth produces is burned, the gas formed from its combustion is just that which our fires and our gas-burners yield, and our own bodies too, by the combustion which attends their living; and, says Mr Streeter, 'the old fable of the maiden from whose lips fell diamonds, may have a really scientific basis after all.' It takes immense heat to burn a diamond, and if it were possible to collect the black material which covers the surface during the process, it would be found to be simply soot. The origin of the diamond is still a matter of scientific investigation and dispute; and the various opinions concerning it may be collected under two heads: (1) The diamond is formed immediately from carbon or carbonic acid by the action of heat. (2) It is formed from the gradual decomposition of vegetable matter. The various methods by which the supporters of the respective theories suppose the transformation to have been wrought, are full of interest and suggestion. In Brazil it was discovered that the matrix of the diamond is itacolumite, and it is said that the gems obtained from itacolumite sandstone have rounded angles and corners, whilst those from the sandy schist are perfect crystals. 'If,' says Mr Streeter, 'this be a fact, we must believe that the agency which changed the sandstone into itacolumite acted also on the diamond.'