128 OLIVER C. FARRINGTON 



constituents, disintegrate and decay far more rapidly than the 

 metallic. The metallic meteorites are, therefore, likely to be 

 found long after stony ones of their time have gone to decay. 

 The unusual weight of the metallic meteorites, moreover, and the 

 silvery appearance of their interior, often lead to their being picked 

 up and preserved where the stony meteorites escape observation. 

 That the metallic meteorites are much more likely to be found 

 than the stony, is indicated by the fact that of 263 meteorite 

 "finds" now preserved in collections, 205 are wholly metallic, 28 

 largely so and only 30 are stony. To determine the average specific 

 gravity of meteoric matter by striking an average of meteorites 

 preserved in collections, seems, therefore, manifestly incorrect. 



The amount of the correction which, according, to Greg 

 should be made for meteoric matter that does not reach the 

 earth in an entire or tangible state, must be at best a matter of 

 speculation. I am of the opinion that the amount of such 

 meteoric dust which reaches the earth is small, for few traces of 

 it have ever been found. Since its amount is probably small and 

 its specific gravity can only be guessed, 1 have thought it safe 

 to omit it altogether from the calculation. 



Considering, then, the desirability of using as many data as 

 possible while at the same time excluding all that might be mis- 

 leading, I can think of no better method of arriving at the desired 

 result than to determine the average specific gravity of the 

 meteorites observed to fall during the past one hundred years, 

 this being the period within which a fairly complete record of 

 meteorite falls has been kept. Such a method, will, of course, 

 exclude a large number of metallic meteorites with high specific 

 gravity, for only seven, or at most eight, of these have been 

 known to fall within the past century. But it is not unreason- 

 able to suppose that these may represent the proportion of iron to 

 stone falls in all periods of the earth's history ; for, as has been 

 stated, the iron meteorites found may have endured for many cen- 

 turies, while the stony ones of similar epochs have gone to decay. 



Greg^ has considered the proportion of stone to iron falls to 



' London Phil. Mag., 4th Sen, Vol. VIII, p. 453. 



