548 



METEORS AND METEORITES. 



thus 95.55 kilom. = 60 miles nearly. The rel- 

 ative frequency of meteor-paths in different 

 parts of the visible heavens varies in the main 

 with the zenith. distance only; and about 1 in 

 50 of all shooting stars seen at a place should 

 have the middle points of their apparent paths 

 within 10 of the zenith. The number of shoot- 

 ing stars visible within a given period over the 

 whole earth is to be considered as 10,460 times 

 the number visible at one- place. Admitting 

 that one observer will see an average of 7-J me- 

 teors per hour, and that the number visible at 

 one place is at least 4 times this, we have then 

 the whole number of meteors that traverse the 

 atmosphere daily, and that sun, moon, and 

 clouds permitting should be visible, to the 

 naked eye, equal to 10,460x7^x4x24, or 

 more than seven and a half millions. Of 1,016 

 paths, the mean length was found to be 12'.6. 

 The meteor-yielding mass, before it has become 

 luminous by entering the earth's atmosphere, 

 the author terms a meteoroid. Now, taking 

 into account the much greater number of shoot- 

 ing stars visible with the telescope than with 

 the naked eye, say 1,582 hourly with a comet- 

 seeker, if the whole heavens could be watched, 

 we* have for the whole number of meteoroids 

 coming daily into the air, at least 10,460 x 1,582 

 x 24=more than 400,000,000 ! The mean actual 

 length of the visible part of meteor-paths is 

 found from the data under consideration to be 

 less than 65, and greater than 39 kilometres; 

 the smaller of the two limits being probably 

 nearest the truth. The mean duration of 368 

 meteors observed at Geneva, Switzerland, in 

 one night, was 0.49 sec. ; that of 499 estimates 

 made in August and November, 1864, 0.418 

 sec. ; mean of the 867 flights, 0.45 sec. From 

 such length of path, and duration, may be in- 

 ferred a mean actual velocity of between 78 and 

 130 kilometres per second, the least of these 

 (more than 48 miles) being twice and a half 

 the velocity of the earth in its orbit about the 

 son. This doe$ not seem consistent with the 

 supposition that most of the meteoroids move 

 in closed orbits about the sun ; but qualifying 

 considerations are introduced, as that the as- 

 sumed altitudes maybe too great, the estimated 

 times too small, etc. At least three supposi- 

 tions respecting the distribution of orbits of 

 meteoroids are naturally suggested : 



"1st. They may form a number of rings, like 

 the August group, cutting or passing near the 

 earth's orbit at many points along its circuit. 

 The sporadic shooting stars may be outliers of 

 such rings. 



" 2d. They may form a disc in or near the 

 plane of the orbits of the planets. 



" 3d. They may be distributed at random, like 

 the orbits of comets. 



" According to the first of these suppositions, 

 there should be a succession of such radiants, 

 corresponding to the several rings. Dr. Ilcis 

 and Mr. Greg believe that they have detected 

 such a series." 



It may here be remarked that some writers 



have admitted as already determined 56 radiant 

 points of shooting stars, corresponding to as 

 many known epochs in every year, and in which 

 meteors proceeding from those definite positions 

 in the heavens may be expected to be visible. 

 Prof. Newton's discussion of the subject, how- 

 ever, leads him, in view of the apparent distri- 

 bution of meteors throughout the 24 hours (that 

 is, as entering the atmosphere from all direc- 

 tions in space), and in view of the seeming fact 

 that their mean velocity considerably exceeds 

 that of the earth, to conclude though not yet 

 with absolute certainty that the orbits of the 

 sporadic meteors generally, are not approxi- 

 mately circular, but that they resemble more 

 the orbits of the comets. 



Finally, apart from the space occupied by our 

 atmosphere, there are in the mean, in each 

 volume of the size of the earth, of that space 

 which the earth is traversing in its orbit about 

 the sun, as many as 13,000 small bodies, each 

 body such as would furnish a shooting star vis- 

 ible under favorable circumstances to the naked 

 eye ; while, if telescopic meteors were counted, 

 the number would be increased at least forty- 

 fold. It is not probable that the space near 

 the earth's orbit is much more thickly strewn 

 with these bodies than other parts of the solar 

 system. Their velocity, different from that of 

 the earth, implies that they are not grouped 

 closely about the earth's orbit. These bodies 

 cannot be regarded as the fragments of former 

 worlds, but are rather the materials from which 

 the worlds are forming. It may here be added, 

 that some writers have regarded meteoroids, at 

 least those large and compact ones which reach- 

 ing the earth constitute meteorites thoso 

 "pocket-planets," as Humboldt has termed 

 them as being portions scattered by the dis- 

 ruption of parent planets which were too small 

 and powerless to reclaim their own fragments. 



Accountsand Descriptions of Some Meteorites, . 

 mostly recent. In the Philos. Magaz., new 

 series, vol. xxviii., will be found an account, 

 by Dr. Haidinger, of the meteorite of Albereto, 

 in the Modenese, and in relation to which 

 falling in July, 1766 a pamphlet has been left 

 by Troili. This contained disseminated through 

 it grains of the native protosulphide of iron, 

 since named Troilite. In the same volume ap- 

 pears a notice by Maskelyne of a meteorite fall- 

 ing, June 16, 1860, near the village of Kusiali 

 in India, and which contained much of the white 

 flocculence abounding in some only of these 

 bodies; and also; an abstract of a paper by Mr. 

 II. C. Sorby, on the mineralogical structure of 

 meteorites. An article on the physical history 

 of meteorites appears also, along with a repub- 

 lication of that last named, in the Amcr. Jour, 

 of Science, January, 1866. 



In the Amer. Jour, of Science, vol. xxxvii. 

 (1864), will be found the analysis, by Prof. C. 

 A. Joy, of New York, of a meteorite from 

 Chili (noticed also in vol. xxxviii., p. 3Sfi); 

 while in the volume last mentioned win al.su 

 be found accounts, including analyses, of sev- 



