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THE POPULAR SCIENCE MONTHLY. 



our atmosphere, this velocity is destroyed 

 by the resistance, and, according to well- 

 known laws, their energy of motion is con- 

 verted into heat of intensity sufficient to 

 render them incandescent, and even to dis- 

 sipate 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 calcu- 

 lation is carried out for the whole earth, al- 

 lowing that at each station all are observed 

 which come within a circle two hundred 

 miles in diameter, the total number reach- 

 ing the earth daily is found to be about five 

 million ; indeed, Prof. Newton, who is per- 

 haps 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 re- 

 cent times in respect to these bodies re- 

 mains to be mentioned. It is found that in 

 four well-marked cases the orbits of impor- 

 tant 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, Ly- 

 rids, 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 fila- 

 ments stretching out into space, in the same 

 way as iron-filings, sprinkled on paper, ar- 

 range themselves in lines under the influ- 

 ence of a magnet underneath, each particle 

 attracting the next by virtue of its induced 

 magnetism. Groneman refers the phenom- 

 enon of the aurora to the ignition of this 



cosmical iron-dust in its passage through 

 air, the distinction between this and an or- 

 dinary meteor-shower being that, on account 

 of the filamentous arrangement of the par- 

 ticles 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 over- 

 head. 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 at- 

 traction 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 in- 

 terpretation of the results of his investiga- 

 tions. " On the contrary," writes Dr. Rob- 

 erts, " the weight of my experiments is en- 

 tirely against him " (Bastian), " and in fa- 

 vor 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 or- 

 ganic 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, hav- 

 ing 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 preexisting 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 in- 

 fusions ; 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 



