In view of the extreme rarity and costliness of radium, it is evident that its emanations may be put to many important uses in and out of the laboratory, since they bestow upon indifferent objects--a plate, a piece of iron, an old shoe, anything--the very properties of radium itself. Thus a scientist or a doctor unable to procure the metal radium may easily experiment with a bit of wood or glass rendered radio-active--that is, charged by radium emanations, and capable of replacing the original metal as long as the charge keeps its potency. This period has been determined by the Curies after observations extending over weeks and months, and applied to all sorts of substances, copper, aluminium, lead, rubber, wax, celluloid, paraffin, no fewer than fifty in all, the resulting conclusions being formulated in a precise law as follows:-- (1) All substances may be rendered radio-active through the influence of radium emanations. (2) Substances thus influenced retain their induced radio-activity very much longer when guarded in a small enclosure through which the emanations cannot pass (say a sealed glass tube) than when not so guarded. In the former case their radio-activity diminishes one-half every four days. In the latter case it diminishes one-half every twenty-eight minutes. I must pass rapidly over various other wonders of radium that M. Curie laid before me. New matter is accumulating every week as the outcome of new investigations. Even in the chemistry of radium, which is practically an unexplored field, owing to the scarcity and costliness of the metal, there are various facts to be noted, as these: that radium changes the colour of phosphorus from yellow to red; that radium rays increase the production of ozone in certain cases; that a small quantity of radium dissolved in water throws off hydrogen constantly by causing a disintegration of the water, the oxygen released being absorbed in some unknown molecular combination. Also that a solution of radium gives a violet or brownish tint to a glass vessel containing it, this tint being permanent, unless the glass be heated red hot. Here, by the way, is an application of importance in the arts, for radium may thus be used to modify the colours of glass and crystals, possibly of gems. It is furthermore established that radium offers a ready means of distinguishing real from imitation diamonds, since it causes the real stones to burst into a brilliant phosphorescence when brought near them in a darkened room, while it has scarcely any such effect upon false stones. M. Curie made this experiment recently at a reception in Lille, to the great delight of the guests. Coming now to what may be the most important properties of radium--that is, those which influence animal life--we may follow M. Curie's advice and visit the Pasteur Institute, where for some months now a remarkable series of radium tests has been in progress.