52 THE POPULAR SCIENCE MONTHLY. 



taken endeavor to make them parts of a general theory on the same 

 scale in regard to details. A specialist, striving to generalize, nearly 

 always goes more or less astray ; but, instead of following him, even 

 though with the idea of setting him right, it is best to take the special 

 results he has obtained at the cost of much labor and research. If we 

 do this with the work of all who have dealt specially with a subject, 

 the chances are that we shall find we have gathered nearly enough 

 to indicate a general theory, which shall include all these specially 

 ascertained details. This the true theory, whatsoever it may be, should 

 unquestionably do. My theory, at any rate, has been obtained in this 

 way, and is intended in its wide generality to cover all the known 

 facts. 



So much premised, I note that my reasoning on the subject of comets 

 and meteors starts from the idea which Professor Newton seems very 

 properly to regard as almost necessarily true, that shooting-stars, fire- 

 balls, aerolites, and in fine all orders of meteoric bodies, belong to the 

 same general class, differing only inter se in size, distribution, orbital 

 motion, and the pi-oportions in which the materials constituting them 

 are distributed. It appears to me, as it does to him, that a theory 

 which will account for such streams as supply the August and Novem- 

 ber displays, but not for the meteoric masses w T hich fall sporadically, 

 can not be the true general theory of meteors ; nor can any theory be 

 accepted as at once true and general which accounts for the holosider- 

 ites while it leaves unexplained the asiderites (so called, though in 

 reality no meteors are free from iron). Again, noting that meteors 

 have been associated with comets, we require for any theory which 

 shall be accepted as generally true, that while it shall explain this con- 

 nection between streams of bodies producing falling stars and certain 

 special comets, it shall also be able to account for all comets as possi- 

 bly associated with meteor-streams, and for all meteor-streams as pos- 

 sibly associated with comets. How much resides in this last condition, 

 those only can guess who have put the matter to the test by striving 

 to find a general theory of comets and meteors which shall not be 

 found to be in conflict with some fact known about particular comets 

 or some other fact known about particular meteor systems. Yet no 

 general theory of comets and meteors can possibly be accepted which 

 fails when thus tested, trying though the test may be. These trying 

 tests are, indeed, particularly valuable for the seeker after truth, seeing 

 that they serve to diminish his field of research by fencing out por- 

 tions which can not usefully be dealt with. My own experience has 

 convinced me that negative indications serve often to lead more di- 

 rectly to the truth than the most seemingly decisive evidence of the 

 positive sort, though in reality it is by combining the two kinds of 

 evidence, rejecting because of decisive negative evidence theory after 

 theory from among those to which we are directed by decisive posi- 

 tive evidence, that we can alone hope to arrive at the true theory. 



