[bowman] fundamental PROCESSES IN HISTORICAL, SCIENCE 505 



been sufficiently, though not as yet accurately, adjusted to prevent 

 similar failures. 



(b) Where differentiation is impossible: In experience it has 

 been found that the thumb prints of two persons are never exactly 

 alike, and for this reason an exact similarity of thumb prints has been 

 accepted in experience as a correct process of identification. If, now, 

 contrary to all previous experience, a case should be found in which 

 the thumbs of two persons would make exactly similar prints, a fail- 

 ure would be established against thumb print identification as a cor- 

 rect process. Such a failure could not be differentiated because no 

 controllable cause could be located for a failure due to a highly ex- 

 ceptional recurrence in nature. The process of thumb print identi- 

 fication, therefore, in view of such a case, could not be so adjusted as 

 to prevent similar failures, but would be condemned scientifically 

 and would have to be abandoned, save as a corroboration of other 

 evidence. A conviction in capital cases would be impossible on thumb 

 print evidence alone. Such a case was thought to have been dis- 

 covered in England in 1911, but this was subsequently disproved. 

 (See, on this case, Appendix B in the author's paper on the Origin 

 and Treatment of Discrepancy in Trustworthy Records in the Trans- 

 actions of the Society for 1911, vol. v, p. 176). 



The 4th methodic principle is akin to the 4th fundamental prin- 

 ciple of science (See Part I, p. 141) in so far as they are both govern- 

 ing principles in actual intercourse, and are capable of illustration 

 by examples drawn from that field. The 4th fundamental principle, 

 however, governs the relations of men in their ordinary course, and is 

 capable, therefore, of well nigh endless illustration; but on the con- 

 trary, the instances where processes previously found correct in 

 experience fail under proper application constitute a great exception, 

 and illustrations of the 4th methodic principle are correspondingly 

 rare. The activity of the one principle is continuous, that of the 

 other occasional; yet where occasion demands, the application of the 

 4th methodic principle is as necessary and certain as that of the other, 

 and, in fact, from the field of correct mechanisms, illustrations may be 

 obtained of the daily application of a principle which is practically 

 the same as the 4th methodic principle. A correct mechanism is a 

 mechanical process that rightly operated leads necessarily to 

 correct results, and where such a mechanism is self-operating, it con- 

 stitutes a correct process in itself. One of the commonest and best 

 examples of such a mechanism is an ordinary watch that is kept 

 in proper order and wound. A watch in this condition necessarily 

 measures time correctly, and if it has proved correct in the owner's 

 experience, he will be governed by it concerning the most important 



