546 



METEOKS AND METEORITES. 



Mr. Glaisher names the 2d of January, the 10th 

 and 20th of April, the 30th of November, and the 

 Ctli of December. Mr. Greg (quoted in Amer. 

 Jour, of Science, xxxvii. 445) states that the 2d 

 of January is as prolific, for several of the 

 24 hours during which it lasts, as is the period 

 of August 9th and 10th, the radiant being about 

 the head of Bootes; that for the 9th-15th of 

 February the radiant is in Leo Minor ; that for 

 a moderate number of meteors of very low 

 velocity, of March 6th-10th, a radiant exists 

 in the head of Lynx; and that for the 5th- 

 13th of December, showing of late years a fine 

 shower, a radiant appears half way between 

 a Gemini and /? Aurigse. He states also that the 

 meteors of the Nov. 13th-14th period are not 

 visible in Australia, while those of the August 

 and other periods are so. The subject of radi- 

 ants will be again referred to. 



Tables of Meteors, and Question of Altitudes. 

 Various estimates of the heights, at appear- 

 ance and disappearance, of meteors, are given 

 in connection with the question of the height of 

 the atmosphere, in the article ATMOSPHERE ; the 

 conclusions therein stated being to some extent 

 those of Prof. Newton's paper (with tables, 1798 

 to 1863), in the Amer. Jour, of Science, July, 

 1864 ; and of his article on the altitudes of the 

 November and August meteors, 1863, in the 

 same journal, September, 1865. Mr. A. S. Her- 

 * schel gives, for meteors observed at five stations 

 in England, August 9th-10th, 1863, the averages 

 of the estimated heights as 82 J and 58 miles ; 

 length of paths, from 18 to 100 miles; dura- 

 tions, from -J to 3 seconds ; velocities, from 23 

 to 71 miles a second. 



Incandescence and Dissipation of Meteors. 

 It has already become generally admitted by 

 physicists that the explanation of the incandes- 

 cence of meteoric bodies, and of that dissipation 

 of their substance which occurs in much the 

 greater proportion of instances, is to be found in 

 the law of the convertibility and definite equiva- 

 lence of mechanical and certain other forms of 

 force, with heat. Thus, every unit of mechani- 

 cal force (equal to a lift of 772 pounds avoirdu- 

 pois through one foot height, at the sea-level), de- 

 stroyed as motion by friction or other obstacle, 

 generates a unit of heat (equal to that which can 

 warm one pound avoirdupois of water through 

 1 Fahr.). Most of the movements of bodies 

 with which we are familiar are such' as do not 

 suffice to produce appreciable rise of tempera- 

 ture. Moreover, any atmosphere existing at 

 heights of from 50 to 100 miles or more above 

 the earth must be extremely rare. But it ap- 

 pears to be ascertained with certainty, that me- 

 teors, after becoming visible, move through this 

 thin atmosphere at the enormous velocities of 

 from 18 to at least about 70 miles a second ; 

 while the equivalent in heat of their motion 

 varies, not as the simple velocity, but as its 

 square (Faye) ; and evidently, every meteor had 

 a still higher velocity before it became luminous 

 than it has after acquiring such condition. Prof. 

 Bunsen, in course of a paper on the meteoric iron 



of Atacama, calculated the loss of active force 

 during the fall of a solid coming into the terres- 

 trial atmosphere, and with a planetary speed, to 

 be sufficient to heat such body to 1,000,000 C.; 

 so that, if .998 of the entire heat were lost in 

 the ambient medium, such body could stili 

 reach the earth heated to 2.000 C. 



Thus, then, through retardation by direct 

 resistance and by friction, the previously dark 

 and invisible masses of meteoric bodies become 

 suddenly heated to luminosity, usually (it is 

 probable) undergoing a sort of combustion, and 

 leaving behind them trains of the disgregated 

 and glowing particles, until they are completely 

 consumed; sometimes (as would be expected) 

 exploding into fragments ; and sometimes, from 

 large amount of substance, or low velocity, or 

 both, outlasting the action of the air, and 

 reaching the earth in a hot, and perhaps glow- 

 ing condition. Still, the extreme rarity of the 

 atmosphere in the usual meteoric altitudes, 

 compels the adoption of low estimates for the 

 weights of the meteoric bodies. Further, by a 

 law of vision, as well as by diffusion of the 

 glowing material, and perhaps by that of the 

 light also, at the source, there is a tendency to 

 enhance the apparent magnitudes of these ob- 

 jects. Dr. Haidinger suggests that non-produc- 

 tive fire-balls (those not reaching the earth), and 

 shooting stars, are of loosely compacted sub- 

 stance one reason for their not penetrating the 

 atmosphere to greater depths before extinction ; 

 and from the like view also it would follow that 

 their size generally is (for solids) out of propor- 

 tion to their weight. In Mr. Herschel's papei 

 on August meteors of 1863, an attempt is made, 

 by considering the apparent light of meteors, 

 and the amount of coal gas which would yield the 

 same at given distances, in connection also with 

 the estimated velocity of those bodies, to deter- 

 mine the heat developed in the latter, and then 

 from this (in connection, it would appear, with 

 the length of flight) to infer what must have 

 been the masses or weights of the meteors. [R. 

 P. Greg, quoted in American Journal of Sci- 

 ence, xxxvii., 445.] Though such a calculation 

 must proceed upon a large amount of assump- 

 tion, the result, even as an approximation, is 

 still of great interest. And such result, Mr. 

 Greg states, is to place the weights of the bod- 

 ies considered at from 20 grains to 7 Ibs. 

 avoirdupois, an average mass being about 1J 

 Ibs. Mr. Glaisher concludes that the largest 

 of the fire-balls included in his catalogue must 

 have weighed nearly 100 Ibs. 



Herschel has suggested that the principle of 

 dissociation (see CHEMISTBY) may explain the 

 luminous trail of meteoric bodies the violent 

 heat sufficing to suspend chemical affinity at the 

 meteoric surface, while the glowing particles 

 of reduced metals and other elements left be- 

 hind, on cooling to a certain temperature, un- 

 dergo combustion anew, of course giving out 

 additional light from this cause. The spectrum 

 of a brilliant shooting star, near Capella, was 

 recently observed by Herschel. Its slow move- 



