73 8 THE POPULAR SCIENCE MONTHLY. 



iarity in the nature of the rocks of Biela's and Tempel's comets. It 

 is very slender ground upon which to rest a denial of the common 

 nature of objects that are so similar in appearance and behavior as the 

 large and small meteors. 



It may be assumed, then, as reasonable that the shooting-stars and 

 the stone-meteors, together with all the intermediate forms of fire-balls, 

 are like phenomena. What we know about the one may with due 

 caution be used to teach facts about the other. From the mineral 

 and physical nature of the different meteorites we may reason to the 

 shooting-stars, and from facts established about the shooting-stars we 

 may infer something about the origin and history of the meteorites. 

 Thus it is reasonable to suppose that the shooting-stars are made up 

 of such matter and such varieties of matter as are found in meteor- 

 ites. On the other hand, since star-showers are surely related to comets, 

 it is reasonable to look for some relation of the meteorites to the as- 

 tronomical bodies and systems of which the comets form a part. 



This common nature of the stone-meteor and the shooting-stars 

 enables us to get some idea, indefinite but yet of great value, about 

 the masses of the shooting-stars. Few meteoric stones weigh more 

 than one hundred pounds. The most productive stone-falls have fur- 

 nished only a few hundred pounds each, though the irons are larger. 

 Allowing for fragments not found, and for portions scattered in the 

 air, such meteors may be regarded as weighing a ton, or it may be 

 several tons, on entering the air. The explosion of such a meteor is 

 heard a hundred miles around, shaking the air and the houses over the 

 whole region like an earthquake. The size and brilliancy of the flame 

 of the ordinary shooting-star are so much less than those of the stone- 

 meteor that it is reasonable to regard the ordinary meteoroid as weigh- 

 ing pounds, or even ounces, rather than tons. 



Determinations of mass have been made by measuring the light 

 and computing the energy needed to produce the light. These are to 

 be regarded as lower limits of size, because a large part of the energy 

 of the meteors is changed into heat and motion of the air. The smaller 

 meteors visible to the naked eye may be thought of without serious 

 error as being of the size of gravel-stones, allowing, however, not a 

 little latitude to the meaning of the indefinite word gravel. These 

 facts about the masses of shooting-stars have important consequences. 



The meteors, in the first place, are not the fuel of the sun. We 

 can measure and compute within certain limits of error the radiant 

 energy emitted by the sun. The meteoroids large enough to give 

 shooting-stars visible to the naked eye are scattered very irregularly 

 through the space which the earth traverses, but in the mean each is 

 distant two or three hundred miles from its near neighbors. If these 

 meteoroids supply the sun's radiant energy, a simple computation 

 shows that the average shooting-star ought to have a mass enormously 

 greater than is obtained from the most prolific stone-fall. Moreover, if 



