Page:Popular Science Monthly Volume 9.djvu/664

638 our atmosphere, this velocity is destroyed by the resistance, and, according to well-known laws, their energy of motion is converted into heat of intensity sufficient to render them incandescent, and even to dissipate any solid portions in vapor. Their numbers are very great. About forty per hour is a fair average for one station, or nearly one thousand each day. If the calculation is carried out for the whole earth, allowing that at each station all are observed which come within a circle two hundred miles in diameter, the total number reaching the earth daily is found to be about five million; indeed, Prof. Newton, who is perhaps the highest authority on this subject, sets the number still higher, at seven and a half million. A curious fact is, that the hourly numbers increase from sunset to sunrise by some fifty per cent. The reason is simply that in the evening we are, so to speak, behind the earth as it rushes through space, and see only those which overtake us; in the morning, on the other hand, we are in front, and see all we meet, as well as those we overtake.

The most remarkable discovery of recent times in respect to these bodies remains to be mentioned. It is found that in four well-marked cases the orbits of important meteoric swarms coincide exactly with the orbits of well-known comets; that the swarm of meteors follows in the wake of the comet and is somehow connected with it. The discovery dates from 1866, when Schiapparelli first proved the connection between the Leonids (November meteors) and Temple's comet. Since then the same thing has been shown of the Perseids, Lyrids, and Bielids.

Cause of the Aurora.—According to Groneman's hypothesis, an account of which is given in the Academy, there are streams of minute iron particles circulating around the sun like the well-known meteor-streams, and these, when they come near the earth, are attracted by its poles, and form filaments stretching out into space, in the same way as iron-filings, sprinkled on paper, arrange themselves in lines under the influence of a magnet underneath, each particle attracting the next by virtue of its induced magnetism. Groneman refers the phenomenon of the aurora to the ignition of this cosmical iron-dust in its passage through air, the distinction between this and an ordinary meteor-shower being that, on account of the filamentous arrangement of the particles in the direction of the dipping needle, streamers are formed, which by an effect of perspective appear to radiate from a point in that direction, and therefore nearly overhead. It is necessary to suppose that this meteor-stream is traveling nearly in the same direction as the earth, and Groneman enters into elaborate calculations to show that the velocity of the particles would not be too great to permit the magnetic attraction to form filaments of 200 miles in length.

Dr. Roberts on Spontaneous Generation.—Dr. William Roberts, of Owens College, Manchester, whose experiments were quoted by Dr. Bastian, in a recent communication, as favoring the doctrine of the spontaneous generation of bacteria, contradicts this interpretation of the results of his investigations. "On the contrary," writes Dr. Roberts, "the weight of my experiments is entirely against him" (Bastian), "and in favor of Pasteur's conclusions. It appears to me," he adds, "that the attitude of Dr. Bastian on the question of the origin of bacteria arises from what I may call the inverted significance which he attaches to the two contrasted results—barrenness or fertility—which follow after boiling an organic infusion. Throughout the controversy Dr. Bastian speaks of the barren tubes and flasks as 'failures,' or 'negative results;' and he evidently regards the fertile tubes and flasks as 'successful' experiments, having the force and authority of 'positive' results. The true view is just the reverse of this: it is the barren flask that has the character of a positive result. For what does the experimenter set himself to do in these experiments? He seeks to destroy, by boiling, all preëxisting bacteria in these infusions, and to leave unimpaired their powers of promoting the growth of bacteria. And it is found, in fact, that this latter quality is perfectly preserved in boiled infusions; for they breed bacteria with the utmost luxuriance when they are reinfected from an extraneous source. . . . When I take up one of the flasks or bulbs which have remained barren in my chamber for