3 88 THE POPULAR SCIENCE MONTHLY. 



The circumstance that most meteors are extinguished before reach- 

 ing the earth seems to show that their mass is but small. If the dis- 

 tance of a meteor from the earth be ascertained, as well as its apparent 

 brightness as compared with that of a planet, it is possible, by compar- 

 ing its luminosity with that of a known quantity of ignited gas, to es- 

 timate the degree of heat evolved in the meteor's combustion. As this 

 heat originates from the motion of the meteor being impeded or inter- 

 rupted by the resistance of the air, and as this motion or momentum is 

 exclusively dependent on the speed of the meteor as well as upon its 

 mass, it is possible, when the rate of motion has been ascertained by 

 direct observation, to determine the mass. Prof. Alexander Herschel 

 has calculated by this means that those meteors of the 9th and 10th 

 of August, 1863, which equalled the brilliancy of Venus and Jupiter, 

 must have possessed a mass of from five to eight pounds, while those 

 which were only as bright as stars of the second or third magnitude 

 would not be more than about ninety grains in weight. As the great- 

 er number of meteors are less bright than stars of the second magni- 

 tude, the faint meteors must weigh only a few grains, for, according to 

 Prof. Herschel's computation, the five meteors observed on the 12th of 

 November, 1865, some of which surpassed in brilliancy stars of the 

 first magnitude, had not an average weight of more than five grains.; 

 and Schiaparelli estimated the weight of a meteor from other phe- 

 nomena to be about fifteen grains. The mass, however, of the mete- 

 oric stones which fall to the earth is considerably greater, whether 

 they consist of one single piece, such as the celebrated iron-stone dis- 

 covered by Pallas in Siberia, which weighed about 2,000 pounds, or of 

 a cloud composed of many small bodies which penetrate the earth's 

 atmosphere in parallel paths, as shown in Fig. 1, and which, from a 

 simultaneous ignition and descent upon the earth, present the appear- 

 ance of a large meteor bursting into several smaller pieces. Such a 

 shower of stones, accompanied by a bright light and loud explosion, 

 occurred at L'Aigle, in Normandy, on the 26th of April, 1803, when 

 the number of stones found in a space of 14 square miles exceeded 

 2,000. In the meteoric shower that fell at Kuyahinga, in Hungary, on 

 the 9th of June, 1866, the principal stone weighed about 800 pounds, 

 and was accompanied by about a thousand smaller stones, which were 

 strewed over an area of 9 miles in length by Z\ broad. 



It must not be supposed, however, that the density of such a cos- 

 mical cloud is as great when out of the reach of the attraction of the 

 sun and the earth as when its constituents fall upon the earth's sur- 

 face. Schiaparelli calculates, from the number of meteors observed 

 yearly in the month of August, that the distance between any two 

 must amount, on the average, to 460 miles. As the cosmical clouds 

 which produce the meteors approach the sun in their wanderings from 

 the far-off regions of space, they increase in density some million times, 

 therefore the distance between any two meteors, only a few grains in 



