346 ANNUAT. OF SCIENTIFIC DISCOVERY. 



read, that it must be accepted with caution ; but there ai'e addi- 

 tional reasons that tlie su!)ject should be well inquired into. 



The next contribution to our knowiediri' of lliese subjects we 

 owe to Mr. Newton, in a paper read before the American National 

 Academy of Sciences. Among the questions dealt with are the 

 number of shooting stars that come into our atmosphere each day, 

 the number of telescopic shooting stars, and the dislril)ulion of 

 the orbits of the meteoroids in the solar system. lie linds that 

 the average number of meteors which traverse the atmosphere 

 daily, and tliat are large enough to be visible to the naked eye, on a 

 dark, clear night, is no less than 7,50i),000; and applying the 

 same reasoning to telescopic meteors, their numbers will have to 

 be increased to 400,000,000 ! If allowance be made for the space 

 occupied by the earth's atmosphere, we find that, in the mean, in 

 eacli volume of the size of the earth, of the space wliich the earth 

 is traversing in its orbit about the sun, there are as many as liJ.OOO 

 small bodies, each body such as would furnish a shooting star, 

 visiljle under f:ivoral)le circumstances to the naked eye. If tele- 

 scopic; meteors be counted, this number should be increased at least 

 forty-fold. 



Mr. New^ton remarks with the true caution of a philosopher : — 

 There are at least three suppositions respecting the distribution 

 of tlie orbits of the meteoroids in t lie solar system which ai-e nat- 

 urally suggested. Either of them may be considered as plausible, 

 and one does not exclude another. 



1. They may form a numljcr of rings, like the August group, 

 cutting or passing near tlu; earth's orljit at many points along its 

 circuit. The sporadic shooting stars may be outliers of such rings. 



2. They may form a disk in or near the plane of the orbits of 

 the planets. 



3. They may be distributed at random, like the orbits of the 

 comets. 



According to the first of these suppositions, tltere should be a 

 succession of radiants corresponding to the several rings. Dr. 

 Ileiss and Mr. 11. P. Gregg ijelieve tliat they have detected such a 

 series. 



Observations show a mean velocity greater than that of a para- 

 bolic orbit. We must regard as almost certain (on tlie hypothesis 

 of an equable distribution of the directions of absolute motions), 

 that the mean velocity of the meteoroids exceeds consideralily that 

 of the earth ; that the orbits are not approximately circular, Ijut 

 resemble more the orljits of the comets. 



These bodies cannot be regarded as the fragments of former 

 worlds. They are rather the materials from which the worlds are 

 forming. 



Mr. Herschel has also communicated a paper on the "Progress 

 of JMeteoric Astronomy during the Year 18G3-4 " to the Astron- 

 omical Society. He dwells especially on the very close corre- 

 spondence of the observations undertaken to determine their height. 

 It appears from this comparison that the heights of shooting stars 

 at Rome are sensibly the same as in those latitudes of Northern 

 Europe where shooting stars have chieii}- been observed ; and these 



