The β-rays from radium having like properties to the stream of negative electrons in a radiant matter tube, it was of interest to ascertain if they would exert a like difference on diamond. The diamond glows under the influence of the β-radiations, and crushed diamond cemented to a piece of card or metal makes an excellent screen in a spinthariscope--almost as good as zinc sulphide. Some colourless crystals of diamond were imbedded in radium bromide and kept undisturbed for more than twelve months. At the end of that time they were examined. The radium had caused them to assume a bluish-green colour, and their value as “fancy stones” had been increased. This colour is persistent and penetrates below the surface. It is unaffected by long-continued heating in strong nitric acid and potassium chlorate, and is not discharged by heating to redness. To find out if this prolonged contact with radium had communicated to the diamond any radio-active properties, six diamonds were put on a photographic plate and kept in the dark for a few hours. All showed radio-activity by darkening the sensitive plate, some being more-active than others. Like the green tint, the radio-activity persists after drastic treatment. To me this proves that radio-activity does not merely consist in the adhesion of electrons or emanations given off by radium to the surface of an adjacent body, but the property is one involving layers below the surface, and like the alteration of tint, is probably closely connected with the intense molecular excitement the stone had experienced during its twelve months’ burial in radium bromide. A diamond that had been coloured by radium, and had acquired strong radio-active properties, was slowly heated to dull redness in a dark room. Just before visibility a faint phosphorescence spread over the stone. On cooling and examining the diamond it was found that neither the colour nor the radio-activity had suffered appreciably. BOILING- AND MELTING-POINT OF CARBON On the average the critical point of a substance is 1·5 times its absolute boiling-point. Therefore the critical point of carbon should be about 5800° Ab. But the absolute critical temperature divided by the critical pressure is for all the elements so far examined never less than 2·5; this being about the value Sir James Dewar finds for hydrogen. So that, accepting this, we get the maximum critical pressure as follows, viz. 2320 atmospheres: (5800° Ab.)/CrP = 2.5, or CrP = (5800 Ab.)/2.5, or 2320 atmospheres.