METEORS 



157 



explosions followed, apparently proceeding from 

 a small and lofty cloml, followed by a shower 

 of thousands of stones, one 8 lb. in weight. 

 A large meteorite exploded with prodigious 

 noise over Madrid on 10th February 1896. On 

 April 20, 1870, a mass of meteoric iron more 

 than 7 lb. weight fell at Rowton in Shropshire, 

 accompanied also by an explosion. On September 

 4, 1887, a large aerolite fell at Krasnoslolnxlsk, in 

 the government of Penza. It was accompanied by 

 a loud explosion, and in it (as in some others) were 

 found crystals having all the chemical properties 

 of the diamond. In nearly every one of these and 

 other cases are noticed the following features ( 1 ) 

 a noise, often an explosion; (2)clowd or smoke; (3) 

 partial fusion of the mass or masses, especially on 

 the surface. These indicate that the aerolite by 

 some means is brought to a very high temperature, 

 at least above the melting-point of iron, which often 

 causes it to burst into fragments. Pieces of one 

 which fell in India in 1861, though picked up miles 

 apart, were found by Maskelyne to fit together into 

 one whole, the fractures coinciding. This high 

 temperature, on the surface of the mass, would 

 easily be produced by the compression and friction 

 of the air in the case of a body moving with 

 sufficient velocity. There is no observed connection 

 between aerolites and volcanoes, nor can volcanic 

 agency account for their velocity, and so this simple 

 explanation of aerial friction is now universally 

 accepted. A sufficient velocity is at once guaranteed 

 when we consider aerolites as simply fireball* whose 

 mass and course are snch as to bring them entirely 

 through our atmosphere into contact with the eartll. 

 Meteoric iron is also alloyed with nickel, col>alt, 

 manganese, magnesium, copper, carl>on, and tin, 

 in a manner in which it is not yet found alloyed 

 in terrestrial minerals ; and this also points to its 

 cosmical origin. Altogether twentv-four of the 

 terrestrial chemical elements have been found in 

 aerolites viz. oxygen, hydrogen, chlorine, sulphur, 

 phosphorus, carlxjn, silicon, iron, nickel, cobalt, 

 magnesium, chromium, manganese, copper, tin, 

 antimony, aluminium, calcium, potassium, sodium, 

 lithium, titanium, arsenic, and vanadium. No 

 new element not found on earth has lieen found in 

 them. 



The second class of meteors form fireballs, which 

 appear as brilliantly luminous iMidies, traversing 

 the sky, often with noise, and always with great 

 velocity. Aerolites liefore their fall have often 

 been seen as fireballs, and the substantial unity of 

 the two classes is now almost universally accepted. 

 Fireballs, then, are regarded as aerolites whose 

 mass and course are such that they escape actual 

 contact with the earth. They are much more 

 numerous than aerolites, and are of great variety 

 in velocity, size, and brilliance. On August 18, 

 1783, one of great size traversed the air over 

 Europe, from Shetland to Koine, at a height of 

 50 miles and with a speed of 30 miles per second, 

 giving oil a greater light than the lull moon. 

 More recently, on November 17, 1887, a splendid 

 tpecimen, seen first over the Irish Sea, crossed 

 westwards over Ireland, at a height of probably 

 about 20 miles, and disappeared above the Atlantic. 

 Many hundreds of such, though usuady less 

 brilliant, have been observed. Arago enumerates 

 813. More are constantly Iwing seen. Their 

 height is obtained by comparison of observations 

 at stations widely separated, and from it and their 

 olwerved speed the actual velocity is computed. 

 From a careful comparison of many observations 

 made by a committee of the British Association 

 it appears that in general they appear at a height 

 of !>etween 20 and 130 miles, and have a velocity 

 of Wtween 17 and 80 miles per second, with an 

 average of 34'4 miles per second. Their actual 



size has been enormously overestimated, at 12,000 

 to 100 feet in diameter. The effects of irradiation 

 and the luminous gases discharged during their 

 course no doubt give them an apparent diameter 

 enormously greater than the reality. It is prob- 

 able that in most cases they are much smaller than 

 aerolites. They generally leave behind them in 

 their track a luminous train or ' tail ' which some- 

 times disappears at once, and at other times persists 

 for some minutes after the fireball itself disappears. 

 These ' tails' are variously coloured, according prob- 

 ably to the different chemical constitution of the 

 ' beads.' 



That these bodies originate altogether beyond 

 our earth is evident from several considerations 

 First, no sufficient terrestrial cause has been 

 assigned. It has never been shown that volcanic 

 explosions can communicate to ejected masses tha 

 necessary velocity. No proof has been advanced 

 of the theory that aerolites and fireballs are con- 

 densed in the atmosphere itself. There is no vcl- 

 canic activity on the moon, which might proiecS 

 such masses beyond the influence of her feebler 

 gravity so as to enable them to fall upon our earth. 

 Kven if there were such activity in our satellite, 

 the velocity of projection required is so great as to 

 place such a cause outside consideration. Secondly, 

 no good reason can be advanced anaitist the theory 

 of cosmical origin. That numerous masses, of 

 various sizes, are in motion through interplanetary 

 space is not in itself improbable, and is established 

 by the investigation of the po-ths and velocities of 

 shooting-stars. Thirdly, the velocity of fireballs, 

 averaging 34 ~4 miles per second, is only comparable 

 with such velocities as that of the earth in its 

 orbit, which is 18~2 miles per second, or of Sinus 

 (see STARS) in its orbit, and those of other planets 

 and stars. It is a velocity not on the terrestrial 

 but on the cosmical scale. Fourthly, there is no 

 special line to be drawn between fireballs and 

 m'eteors, luminous bodies of all degrees of size be- 

 tween the smallest meteor and the fireball having 

 been observed. It is in fact sometimes a matter or 

 doubt to the observer to which class he should 

 relegate an observed example. To regard all as of 

 common extra-terrestrial origin is then reasonable, 

 and this view is now adopted almost universally. 



We are then led onwards to the consideration of 

 shooting-stars, as both the most numerous class of 

 these appearances, and that class by observing 

 which a satisfactory explanation of them all has 

 ultimately been readied. On any fine night a, 

 watcher who is careful and patient for a sufficient 

 time will see some of these, but occasionally they 

 are much more numerous. On these occasions 

 they are noted as originating all in one or more 

 distinctly marked parts of the sky. From their 

 point of origin they appear to radiate, and if it be 

 overhead, and the meteors very numerous, the 

 appearance is like an ' umbrella of fire ' above the 

 earth. But this point may not be overhead. It 

 may even l>e below the horizon. In the latter case 

 the meteors appear to come up over the horizon 

 like rockets and ascend into the sky. This 

 'radiant, 'as it is technically called, remains fixed 

 among the stars, so that if at the beginning of an 

 observation it be overhead, it will perhaps be below 

 the horizon before the observer ceases his work. 

 It is either named from the constellation in which 

 it is placed, or indicated by its north polar dis- 

 tance and declination on the sphere of the heavens. 

 Meteors from more than one radiant are frequently 

 passing at the same time, but usually each radiant 

 sends forth a particular kind. Leonids (i.e. the 

 meteors whose radiant is in Leo), or the famous 

 November meteors, are bright and swift, leaving 

 very durable tracks of light. The Taurids (from 

 constellation Taurus) give us many fireballs. Other 



