6 



SCIENCE. 



[N. S. Vol. III. No. .53. 



test perhaps the most that can be said is 

 that it is a test by quantities, and that the 

 experienced investigator, having previously 

 found relations of quantity the most satis- 

 factory criteria, habitually employs them 

 whenever the circumstances permit. 



Again it occurred to me that the stellar 

 body would presumptively be composed, 

 like the smaller masses round about, of 

 iron, and that its presence or absence 

 might, therefore, be determined by means 

 of the magnetic needle. If it were absent 

 the compass would point in the same direc- 

 tion, whatever its position with reference 

 to the crater, whether within or without, 

 on one side or the other, near by or miles 

 away ; but if a mass of iron large enough 

 to produce the crater lay beneath it its at- 

 traction would pull the needle one M^ay or the 

 other, producing local variations. Doubt- 

 less the suggestion of this test came from 

 knowledge of the methods emploja^d in 

 searching for magnetic iron ore in northern 

 Michigan, where the prospector carries the 

 dip needle to and fro through the forest, and 

 by means of its changes of direction deter- 

 mines the position and extent of bodies of ore. 



As an equipment for these measurements 

 I provided myself with the instruments nec- 

 essary to make an accurate topographic map, 

 and obtained, through the courtesy of the 

 Coast and Geodetic Survey, a full set of in- 

 struments for the observation of terrestrial 

 magnetism. I was so fortunate, also, as to 

 secure the cooperation of an expert mag- 

 netic observer, Mr. Marcus Baker, of the 

 Geological Survey, and together we set out 

 for Arizona. 



At this time it seemed to me that the 

 presumption was in favor of the theorj'- 

 ascribing the crater to a falling star, be- 

 cause that theory explained, while its 

 rival did not, the close association of the 

 crater with the shower of celestial iron. So 

 far as we know, a falling meteor is just as 

 likely to reach any one spot on the earth's 



surface as any other, and it is, therefore, 

 entirely possible that the coincidence of the 

 meteoric locality with the locality of the 

 crater has no special significance; but if 

 the two phenomena are not connected by a 

 causal relation, it is no more probable that 

 the crater should coincide in place with one 

 of the 165 meteoric falls recorded within the 

 bounds of the United States than that it 

 should occupy anj' other spot of our broad 

 domain. A rough estimate shows the prob- 

 ability of non-coincidence to be at least SOO 

 times as great as the probability of coin- 

 cidence. This by no means warrants the 

 conclusion that an explanation ascribing a 

 causal relation is SOO times as probable as 

 one ascribing fortuitous coincidence, but 

 it legitimately inclines the mind toward 

 causality in the absence of more du-ect and 

 authoritative evidence. 



This point is illustrated by the investiga- 

 tion of the peculiar skj' colors observed 

 twelve yeai« ago. Considering the phe- 

 nomenon of coloration in its entiretj' — char- 

 acter, distribution and duration — it was not 

 merelj' rare, it was unique. In the same 

 year a tremendous volcanic explosion oc- 

 curred in the Straits of Sunda, and that 

 also was unique in intensitj^ The coinci- 

 dence of the two, which in this case was a 

 matter of time rather than place, led to the 

 belief that the one was caused by the other, 

 and this belief was held by many men of 

 science before an adequate explanation of 

 the mode of causation had been suggested. 



So when Mr. Baker and I started for the 

 crater it seemed rather probable than other- 

 wise that we should find a local deflection 

 of the magnetic needle, and that we should 

 find the material of the rim more than suf- 

 ficient to fill the hollow it surrounds. 



Before our journey Avas ended another 

 explanation suggested itself. Mr. Johnson 

 had described the crater as not truly circu- 

 lar but somewhat oval, the longer diameter 

 lying east and west. He noted also that 



