62 POPULAR SCIENCE MONTHLY.
bodies submitted to the rays issuing from radium in a confined space, became active themselves in an analogous manner. On removing the bodies from this influence the power thus excited passes off in accord- ance with a given law independent of the nature of the bodies. In this connection experiments were made with bodies of diverse consti- tution, such as aluminium, copper, lead, bismuth, platinum, silver, glass, alum, parafiine, celluloid and caoutchouc.
Professor Eutherford, of Montreal, has found that this induced activity is produced by an 'emanation' that behaves like a gas, but this gas has not been isolated, or tested chemically or physically. In this connection it is of interest to note that Dr. Giesel, of Germany, also mentions a peculiar, colorless gas, having radio-active properties obtained by the decomposition of radium bromide.
The nature and extraordinary energy of the rays emitted by this singular substance has attracted much attention; it has been shown that they are of different kinds, a part being identical with cathode rays and another part capable of being still further divided into very penetrating rays, and those easily absorbed. Their energy is esti- mated by Rutherford and McClung to be prodigious; they calculate that one gramme of radium would radiate in a year energy equivalent to 3000 gramme-calories, which is about one foot-pound per hour. The source of this energy is a mystery; the savants last named suggest that it is due to the breaking down of atoms into smaller particles which themselves constitute these radiations.
Since it is universally admitted that the radiations are material the problem arises, does radium lose weight in the course of time? This question has been answered differently by two authorities. Bec- querel has calculated from experimental data that one square centi- meter of radium-surface would lose 1.2 milligrammes of matter in one thousand million years. On the other hand, Heydweiller found that five grammes containing only a small percentage of pure radium lost about 0.02 of a milligramme per day, and he observed a total loss of one half milligramme in a time not stated. The excessively small quantities of material available for examination and its exceeding rarity (a very small sample is valued at twenty-five dollars) will ac- count for such contradictory statements.
The discovery by Curie and Laborde that radium emits heat was the result of two experiments. By a thermo-electric method they ascer- tained that a specimen of barium chloride containing one sixth of its weight of radium chloride indicated a temperature 1.5° C. (2.7° Fah.) higher than a sample of pure barium chloride; the temperature was determined by comparing the heat emitted with that excited in a wire of known resistance by an electric current of known intensity. In the second experiment they employed a Bunsen calorimeter. The ex-