AVERAGE SPECIFIC GRAVITY OF METEORITES 12 J 



mean of these two extremes, say, 3.0." As this density is inter- 

 mediate between that of Mars, 5.3, and Jupiter, 1.4, he considers 

 it as confirming the theory that meteorites belong to the series 

 of planets, and have their orbits at a greater mean distance than 

 that of the earth's from the sun. 



A careful consideration of the results above quoted makes it 

 difficult to accept any of them as final. The chief objection to 

 Hill's results lies in the fact that there can be no assurance 

 that the 57 cases which were listed by Flight, represented 

 the average constitution of meteoric matter. Only an average 

 obtained from the largest number of cases possible can be 

 considered trustworthy, even though such an inquiry involve, 

 as Hill states, "enormous labor of research." Again, it should 

 be borne in mind that all the data which can at best be 

 obtained, form but a small part of the whole, so that it is 

 desirable that the relation of this part to the whole should be 

 determined as accurately as possible. Daubree has calculated^ 

 that the fall of a meteorite on some portion of the earth is a 

 phenomenon of daily occurrence, yet the number of observed 

 falls during the past century has averaged not over one for 

 every four months. This gap between possible and observed 

 falls, due, of course, to the fact that a large portion of the 

 earth's surface is covered by water, or is uninhabited by persons 

 capable of intelligent observation, makes the collection of as 

 large a number of data in regard to observed falls as possible, 

 desirable. 



It is only, however, during the present century that any sys- 

 tematic record of meteorite falls has been made at all. To 

 include specimens preserved from earlier falls, is, therefore, 

 likely to weaken rather than strengthen the probability of accu- 

 racy in the average. 



Again, it seems incorrect to include any meteoric "finds" in 

 obtaining data for the desired average. The stony meteorites, 

 owing to the oxidation of the metallic grains which they contain, 

 and the easy decomposability of olivine and others of their mineral 



'Annales des Mines, 1868. 



