604 



NA TURE 



{Oct. 1 8, 1888 



1865, from the duration of the flight of shooting-stars, by Prof. 

 Newton. 1 



From Wartmann's observations of the duration of the flights of 

 368 shooting-stars at Geneva during one night by six observers, 

 a mean was found of 0*495. for each flight. The mean of 499 

 estimates made in August and November 1864 is o*4l8s. The 

 mean duration of the 867 flights iso*45s. 



Prof. Newton remarks : — "A mean duration of half a second, 

 and a mean length of path between 39 and 65 kilometres, imply 

 a mean velocity between 78 and 130 kilometres per second. The 

 smallest of these (more than 48 miles) is twice and a half the 

 velocity of the earth in its orbit about the sun. This cannot con- 

 sist with the supposition that most of the meteoroids move in 

 closed orbits about the sun." 



Both the briefness, however, of this assumed duration, and 

 even the least limit, accordingly, of the velocity so found, were 

 presumed by Prof. Newton to be probably overrated. 



The final step in this demonstration was taken by Schiapa- 

 relli, but before this Newton had distinctly shown that most of 

 the meteors visible were not single in their movements round 

 the sun, but that they belonged to systematic streams and that 

 these streams were not rings. 



With special reference to the November ring, Prof. Schiapa- 

 relli'-' came to the conclusion that the orbit, instead of being 

 nearly circular, as Newton had at first supposed, was very 

 elongated, like those of comets ; and Prof. Adams :! demon- 

 strated shortly afterwards that, among several possible periods of 

 the stream which Prof. Newton had already indicated, the true 

 period was 33*25 years, the demonstration depending upon the 

 increase of the longitude of the node by the action of the planets 

 Jupiter, Saturn, and Uranus, the calculated increase amounting 

 to 28', while the actual increase was 29', and he gave the 

 following elements of the orbit of the swarm — 



Period 



Mean distance 

 Eccentricity 

 Perihelion distance... 

 Inclination ... 

 Longitude of node ... 

 Distance of perihelion from node... 

 Motion retrograde. 



33*25 years (assumed) 

 10*3402 

 0*9047 



o*9855 

 1 6° 46' 

 57-28 

 651 



Aided by considerations suggested by observations of the 

 conditions under which the meteors were observed — from a 

 particular part of the sky, in a particular part of the earth's 

 orbit, at a particular time and from a particular point of the 

 earth's surface,, we can understand at once that it was as practic- 

 able to determine the orbit of the swarm as it is to determine 

 the orbit of a planet or of a comet. 



The final step taken by Schiaparelli, to which we have 

 referred, was a demonstration that the orbits of certain of these 

 streams or swarms, to which reference has been made, were 

 really identical with the elements of known comets. 



Schiaparelli computed the elements of the orbit of the August 

 meteors, supposing them to be moving along a cometary or 

 parabolic orbit. For his calculations the data were the radiant 

 in R.A. 44 , N. Decl. 56°, the time of the earth passing near the 

 centre of the group in 1866, August 10*75. With the elements 

 thus obtained he found those of the comet 1862 III., accord- 

 ing to the latest determinations by Oppolzer, 4 to be nearly 

 identical, as is seen in the following statement : — ■ 



Long, of perihelion 

 Long, of node 

 Inclination 

 Perihelion distance 



Motion 



Perihelion passage 

 Period 



Elements of 

 August Meteors. 



• • U3 38 



.. 138 16 



64 3 

 .. 0-9643 

 .. retrograde 

 .. July 23*62 



Elements of 

 Comet 1862 III. 



344 41 

 137 27 



66 25 



09626 



retrograde 



Aug. 22-9, i860 



123*4 years 



As remarked by Prof. Newton, 5 we come thus to the un- 

 expected conclusion that the comet of 1862 is nothing else than 

 one of the August meteoroids, and probably the largest of them all. 



Silliman's Journal, vol. xxxix. p. 203. 

 '■ 'Bulletino Meteorologico dell' Osservatorio del Collegio Romano, vol. v. 

 i860. 



3 Monthly Notices, vol. xxvi. p. 247, April 1867. 



4 Astr. Nach , No. 1384. 3 Silliman's Journal, vol. xliii., !867. 



When this relation of the comet of 1862 with the August 

 meteors was discovered by Schiaparelli, no comet was known 

 having similar relations with the November meteors. Oppolzer, 

 however, shortly after, 1 published a corrected orbit of comet 

 1866 I., and the resemblance of its elements to those of the orbit 

 of the November group was at once obvious, and attracted the 

 attention of several astronomers. 2 The following table gives the 

 details : — 3 



Since this discovery of Schiaparelli's, one by one the various 

 star showers have been shown to be due to meteorite swarms 

 pursuing generally elliptic orbits round the sun, which orbits are 

 identical with those of various known comets. Hence each 

 " radiant point " is already, or will subsequently be, associated 

 with a comet. 



Distribution of Meteorites in the Solar System. 



The vide planetaire is now ultimately abolished, and we find 

 the solar system to be a meteoritic plenum in which sporadic 

 meteorites and swarms of greater or less density are moving in 

 orbits more or less elongated round the sun. 



The demonstration that meteorites are extra terrestrial bodies 

 has been followed by researches which, as they have become 

 more complete and searching, have gradually driven men of 

 science to increase their estimates, till at last the numbers acknow- 

 ledged to exist in what was formerly supposed to be empty space 

 have become enormous. 



First as to the sporadic meteorites. 



Observations of sporadic falling stars have been used to deter- 

 mine the average number of meteorites which attempt to 

 pierce the earth's atmosphere during each twenty-four hours. 

 Dr. Schmidt, of Athens, from observations made during seven- 

 teen years, found that the mean hourly number of luminous 

 meteors visible on a clear moonless night by one observer 

 was fourteen, taking the time of observation from midnight 

 to 1 a.m. 



It has been further experimentally shown that a large group 

 of observers who might include the whole horizon in their 

 observations would see about six times as many as are visible to 

 one eye. ' Prof.'H. A. Newton and others have calculated that 

 making all proper corrections the number which might be visible 

 over the whole earth would be a little greater than 10,000 times 

 as many as could' be seen at one place. From this we gather- 

 that not less than 20,000,000 luminous meteors fall upon our 

 planet daily, each of which in a dark clear night would present 

 us with the well-known phenomenon of a shooting-star. 



This number, however, by no means represents the total 

 number of sporadic meteorites that enter our atmosphere, because 

 many entirely invisible to the naked eye are often seen in 

 telescopes. It has been suggested that the number of meteorites 

 if these were included would be increased at least twenty-fold ; 

 this would give us 400,000,000 of meteorites falling in the earth's 

 atmosphere daily. 



If we consider only those meteorites visible to the naked eye 

 as sporadic meteors or falling stars, and if we further assume 

 that their absolute velocity in space is equal to that of comets 

 moving in parabolic orbits, Prof. H. A. Newton has shown that 

 the average number of meteorites in the space that the earth 

 traverses is in each volume equal to the earth about 30,000. This 

 gives us as a result in round numbers that the meteorites are dis- 

 tributed each 250 miles away from its neighbours. 4 



1 Astr. Nach., No. 1624. 



2 Peters, Astr. Nach., No. 1624; Oppolzer, ibid., No. 1626; Schiaparelli, 

 ibid. 



3 Bulletino Meteor., February 28, 1867. 



4 Article "Meteorites," Prof. Newton, " Encyclopaedia Britannica," 

 9th edition, vol. xvi. ; and "Abstract of a Memoir on bhooting-Stars," by 

 Prof. Newton {Silliman's Journal, vol. xxxix., 1865). 



