290 WELLS'S NATURAL PHILOSOPHY. 



ber and frequency of occurrence, many careful observations have been made 

 upon them, with a view of determining these facts. 



Their velocity is supposed to range from sixty to fifteen hundred miles per 

 minute. 



Some of these meteoric appearances may bo seen every clear night, but 

 they appear to fall in great numbers at certain periodical epochs. The pe- 

 riods when they may be noticed most abundantly are on the 9th and 10th of 

 August, and the 12th and 13th of November.* 



The majority of shooting stars appear to radiate from 

 a particular part of the heavens, viz., a point in the con- 

 stellation Perseus, undoubtedly far beyond the limits of our 

 atmosphere. 



__.. .... In order to account for the origin of shooting stars, it has 



What theories ° ° ' 



have been pro- been supposed by Prof. Olmstead, that they are derived from 



posed to ac- ^ body composed of matter exceedingly rare, like the tail of a 

 count for the •' ' a j > 



origin of shoot- comet, revolving around the sun •svithin the orbit of the earth, 

 ing stars ? ^^ ^ spaco little less than a year ; and that at times the body 



approaches so near the earth that the extreme portions become detached and 

 drawn to the earth by virtue of its great attraction. It has been further sup- 

 posed that the matter of which these bodies is composed is combustible, and 

 becomes ignited on entering the earth's atmosphere. 



The nearest approach of the central body to the earth is supposed to be 

 about 2,000 miles. Bodies falling from this distance would enter the earth's 

 atmosphere at a height of at least 50 mUes above the surface, with a velocity 

 generated by the force of gravity above 4 miles per second — a velocity tea 

 times greater than the utmost speed of a cannon-balL 



"When common air is compressed in a tight cylinder to the extent of ono 

 fifth of its volume, sufficient heat is generated to ignite tinder. If we suppose 

 that the fragments descend with such velocity as to compress the rarefied 

 atmosphere at the height of 30 miles to such an extent only as to make it as 

 dense as ordinary air, the temperature would be raised as high as 46,000° F. 

 — a heat far more intense than can be generated in any furnace. Unless, 

 therefore, the mass of matter comprising the body was very large, it must bo 

 dissipated by heat long before it reaehes the surface of the earth. 

 • Another theory has been proposed by the eminent astronomer Chaldini, 

 who supposes that, in addition to the planets and their satellites which revolve 

 about the sun, there are innumerable smaller bodies ; and that these occa- 

 sionally enter within the atmosphere of the earth, take fire, or descend to ita 

 surface. 



* They hare also been noticed in unusual abundance on the 18th of October, the 6th 

 and Tth of December, the 2d of January, the 23d and 24th of April, and from the 18th to 

 the 20th of June. 



Four most remarkable meteoric showers hare been noticed, viz., in 1707, 18.^1, 1832, and 

 1833, all in the month of November. In the shower of 1833, the meteors, in many parts of 

 the United States, appeared to fall as thick as snow-flakes. 



