Page:Popular Science Monthly Volume 54.djvu/879

Rh hours. The lamps are said to work equally well with either alternating or direct currents, and there is no vacuum necessary. If this lamp proves a success as a commercial apparatus, it will be but another example of how slight a matter may make all the difference between success and failure. There have been numerous experimenters trying for the last ten years, and in fact ever since the appearance of the arc lamp, to utilize in an electric lamp the great light-giving power of the refractory earths in a state of incandescence; but, owing to their high resistance at ordinary temperatures, no results were obtained until Professor Nernst thought of heating his thoria rod, and this simple procedure seems to have solved the whole difficulty. It is claimed that the Nernst lamp is a much more economical transformer of electricity into light than the present incandescent electric lamps. An apparatus called a kaolin candle, which has been suggested as an anticipation of Professor Nernst's lamp, was constructed by Paul Jablochkoff in 1877 or 1878. It consisted of a strip of kaolin, along which ran a "match" of some conducting material. The current was passed through this "match" until the kaolin strip became heated sufficiently to become a conductor itself. The lamp did not, however, prove a commercial success.

Laws of Climactic Evolution.—The problem of the laws of climatic evolution was characterized by Dr. Marsden Manson, in a paper read at the British Association, as one of the grandest and most far-reaching problems in geological physics, since it embraces principles and laws applicable to other planets than ours. After presenting a formulation of those laws, the author pointed out that in consequence of their working, a hot spheroid rotating in space and revolving about a central sun, and holding fluids of similar properties to water and air within the sphere of its control, must pass through a series of uniform climates at sea level, gradually decreasing in temperature and terminating in an ice age, and that this age must be succeeded by a series of zonal climates gradually increasing in temperature and extent The conclusions thus reached were that in the case of the earth zonal distribution of climates was inaugurated at the culmination of the ice age, and is gradually increasing in temperature and extent by the trapping of the solar energy in the lower atmosphere, and that the rise has a moderate limit; that the ice age was unique and due to the physical properties of water and air, and to the difference in specific heat of land and water; and that prior to the ice age local formation of glaciers could occur at any latitude and period. Dr. Manson then observed that Jupiter was apparently in a condition through which the earth has already passed, and Mars was in one toward which the climatic evolution of the earth was tending.

Poisonous Plants.—Statistics in regard to poisonous plants are lacking on account of a general ignorance of the subject, and it is therefore impossible to form even an approximate estimate of the damage done by them. Besides the criminal uses that may be made of them, there are some other problems connected with them that are of general public interest. The common law of England holds those who possess and cultivate such plants responsible for damages accruing from them; and a New York court has awarded damages in a case of injury from poison ivy growing in a cemetery. In order to obtain information on the subject, the botanical division of the Department of Agriculture arranged to receive notices through the clipping bureaus of the cases of poisoning recorded in the newspapers. Thus through the persons named in the articles or through the local postmaster it was put in correspondence with the physician in the case, who furnished the authentic facts. A large number of correct and valuable data were thus secured. It is proved by these facts that all poisonous plants are not equally injurious to all persons nor to all forms of life. Thus poison ivy has no apparent external effect upon animals, and a few of them eat its leaves with impunity; and it acts upon the skin of the majority of persons with varying intensity—on some hardly at all, while others are extremely sensitive to it. A similar variability is found in the effects of poisonous plants taken internally. In some cases often regarded as of that kind, death is attributable not to any poison which the plant contains, but to immoderate or incautious eating, or to