Page:Popular Science Monthly Volume 11.djvu/134

124 Cent., and then slowly cooled. The resistance increased up to 90°, and thenceforward gradually decreased. In cooling, resistance steadily increased from 200° down to the room-temperature. This increase was so great that at the end of the experiment the resistance was six times what it was at the beginning, temperatures being equal. The same bar having been again heated from 20° to 200° Cent., there was no turning point, and the resistance decreased steadily to the end, and increased continuously throughout in the cooling; but at the end the resistance was less than at the beginning.

Bar 2 behaved essentially like bar 1; the turning-point, however, was much higher, viz., 140°. With bar 3 five series of experiments were made, and with quite similar results. With the first heating there was a turning-point, which did not appear with after-heatings. At the maximum temperature, the resistance was pretty constant, while the resistances at the beginning and end of the experiments were very irregular.

Destruction of Germs at Low Temperatures.—Prof Tyndall, in a communication to the London Royal Society, shows how heat, when discontinuously applied, though the temperature be below the boiling-point of water, effectually sterilizes organic infusions. In all such infusions, he observes, there is a period of latency preceding their clouding with visible bacteria. During this period the germs are being prepared for their emergence into the complete organism. They reach the end of this period of preparation successively, the period of latency of any germ depending on its condition as regards dryness and induration. The author's mode of proceeding is this: Before the latent period of any of the germs has been completed—say a few hours after the preparation of the infusion—he subjects it for a brief interval to a temperature which may be under that of boiling water. Such softened and vivified germs as are on the point of passing into active life are thereby killed; others not yet softened remain intact. This process he repeats well within the interval necessary for the most advanced of those others to finish their period of latency. The number of undestroyed germs is further diminished by this second heating. After a number of repetitions, which varies with the character of the germs, the infusion, however obstinate, is completely sterilized. The periods of heating need not exceed a fraction of a minute in duration. Sum them up in the case of an infusion which they have perfectly sterilized: they amount altogether to, say, five minutes. Boil another sample of the same infusion continuously for fifteen or even sixty minutes, and yet it is not sterilized, although the temperature is higher and its time of application more than tenfold that which, discontinuously applied, infallibly produces barrenness.

Extinction of a Prehistoric Race.—The extinction of the partially civilized race who once dwelt in the Rocky Mountain region was probably the result of some great geological change. The country is naturally arid, but doubtless when this nearly-forgotten people dwelt here in the numerous cities whose ruins are still to be seen the conditions of life were more favorable. The annals of this interesting race have perished with them, and the history of their downfall is now matter for conjecture. Mr. F. S. Dellenbaugh, of the Buffalo Society of Natural Sciences, describes as follows the course of events which resulted in the extinction of the Shinumos: When the change occurred, "the inhabitants, not understanding the science of irrigation, beheld their crops slowly but surely failing every year. The inevitable result was famine. By this their hardy constitutions were weakened, and the way was prepared for some great epidemic that swept away thousands, and left them in a melancholy condition. Then the epidemic was, possibly, soon followed by the appearance of the Indian, so entirely different from the Shinumo. He was ferocious, treacherous, cunning. Lying, cheating, stealing, murdering, were his pastimes. Then, it is no wonder that the Shinumo, in his emaciated condition, was compelled to retreat before the impetuous attack of such a foe. He was no warrior—no hunter. He had depended almost entirely on his knowledge of agriculture for his peaceful existence. It was impossible