1916.] NATURAL SCIENCES OF PHILADELPHIA. 17'. 



yielded hut very slightly to oxidation since it fell upon the earth. 

 It is interesting to note, however, that all of its edges were rounded 

 as if they had been subjected to abrasive action, but it. was n<>t. as 

 perfectly rounded or oval in shape as the great majority of tin- iron 

 meteorites. If it fell at the same time as the cluster which made the 

 crater, as I now think is probable, possibly this was due to the fact 

 that it. had been gathered up by the iron-headed comet in its passage 

 through space and had not been a member of the cluster for as long 

 a time as its iron companions. 



The abrasive action between these masses of meteoric material 

 composing the comet's head, even though it is less than any grinding 

 action that we can conceive of owing to the fact that the mass travels 

 through the ether of space, has, I would suggest, something to do with 

 the visibility of comets. Inconceivably gentle abrasive action may 

 be sufficient to wear off infinitesimal particles of matter, considering 

 the enormous periods of time available. If so, may it not be that 

 the attrition between the masses of meteoric material, for example 

 masses of iron, not only possibly causes a disturbance of the ether 

 where the grinding or milling action takes place, but literally fills 

 the space in and around the head of the comet with exceedingly fine 

 particles of cometary dust? May not these fine particles of matter, 

 possibly electrified, also form the so-called tail as they are swept 

 away from the main body of the comet travelling through space? 

 The explanation of the tail pointing away from the sun is somewhat 

 difficult on this theory, but the difficulty disappears if we can conceive 

 the particles to be so infinitesimally small and so wanting in weight 

 as to be affected by the light waves of the sun and to be driven by 

 them in a direction away from the sun. 



There can be no doubt that all the so-called " shale-ball'' iron 

 meteorites so far discovered by us in the material forming with 

 the upturned edges of the limestone and sandstone strata the rim 

 of the Arizona crater show evidence of what seems to have been 

 abrasive action. The inference is unavoidable that they have been 

 subjected, during perhaps billions of years, to such action, incon- 

 ceivably slight, it is true, but nevertheless sufficient to finally reduce 

 them to the shapes in which we find them. It is evident that the 

 abrasion was not produced by their passage through our air. May 

 they not be in fact "celestial cobblestones," and may not the milling 

 action when they rub against each other, even very gently, account, 

 in some way, not perfectly understood, for not only what we term the 

 brilliant head of a comet but tor its tail as well? 



