130 KEPORT — 1865. 



causing a maximum of temperature on the 3rd of December, which cannot 

 be explained by any regular appearance of meteors at that date. 



M. Le Verrier communicates to the Academy of Paris the observation, at 

 Constantinople, of a black body seen to cross the disk of the sun in forty-six 

 minutes, between 9 h and 10 h a.m. (local time), on the 8th of May 1865. The 

 observation adds interest to the former paper on the remarkable variations of 

 temperature in the months of spring (Comptes Eendus, 1865, May 29). 



(2.) Heights, and Numbers of Meteors (Am. Journ. Sci. vol. xxxix. p. 193, and 

 Mem. Am. Acad. 1864, Aug. 6). 



From the table of heights of meteors contained in the Am. Journ. Sci. (vol. 

 xxxviii. p. 135*), Professor Newton estimates the mean height of the centre 

 of the paths of shooting-stars above the earth to be 95-55 kilometres, or not 

 quite sixty miles (see also ' Les Mondes,' vol. v. p. 756). Their distribution 

 at other altitudes above the earth's surface is plainly indicated by the 

 following Table : — 



From 19 to 38 miles ( 30 kilom. to 60). Total 114 meteors. 

 38 „ 56 „ ( 60 „ 90). „ 243 „ 





56 „ 75 „ ( 90 „ 120). „ 277 



75 „ 94 „ (120 „ 150). „ 106 



94 „ 112 „ (150 „ 180). „ 57 



A consideration of 1393 meteors (recorded by about forty observers) shows 

 that the whole number of meteors visible at one place is 50-35 times the 

 number visible within 10° of the zenith, and therefore 50-35 times the 

 number of meteors occurring within this cone. If m represents the hourly 

 number, N the total number visible over the whole earth in the same time, it 

 is shown from the law of distribution in altitude, already stated, that 



N=10,460xm. 



Thirty meteors per hour in all the sky, concluded from the careful obser- 

 vations of M. Pouvard (Comptes Eendus, xiii. p. 1029), is not too large for 

 the mean value of m. It may therefore be concluded that the average 

 number of meteors traversing the atmosphere daily, and large enough to be 

 seen with the naked eye on a dark clear night, is more than seven and a half 

 millions. 



The number of such meteors traversing a space equal to the sphere of the 

 earth (radius R), at any moment, with an average relative velocity (V), is 



116-2 x y meteors, omitting the effect of the earth's attraction. 



The average length of flight of shooting-stars is 12°-6. The mean distance 

 of the centres from the observer is upwards of ninety miles, the average 

 length of path upwards of twenty-five miles, and the average velocity calcu- 

 lated from a mean duration of 0-45 second, is at least forty-eight miles per 

 second. If, however, the average velocity is only thirty miles per second, it 

 follows from this formula that in each volume of the size of the earth, on 

 the track of its orbit about the sun, there are as many as 13,000 meteoroids, 

 large enough to furnish shooting- stars visible to tbe naked eye. 



Of telescopic meteors, it is shown that their numbers are at least forty-fold 

 as great. 



* Misprinted vol. xxxvi. in Appendix III. of last Report. 



