78 



MEMOIRS OF TUE NATIONAL ACADEMY OF SCIENCES. 



The jndgiiients cnniiciiited witli any ,<jiveii deftrec of confidenee were more likely to be rialit 

 with greater dittereuces thau with smaller ditt'ereuceti. To show this, we give the tVeqiieiicy of the 

 dittereiit marks in Mr. Jastrow's second, third, and fourth groups.* 



The apparatus used was au adaptation of a "Fairbanks" post-oflice scale; upon the end of the 

 beam of which was fixed a square enlargement (about one-half inch square), with a flat tojt, 

 which served to convey the pressure to the linger in a manner to be presently described. This 

 was tightly covered witli an India-rubber cap, to ]n'event sensations of cold, &c., from contact 

 A\ith the metal. A kilogram i)laced in the pan of the balance brought a pressure of one fourtli 



" The rt-snlt of our oliservntions on the confidence connected with the judgments is lis t'ollows: 



[Subject, Mr Peirce.] 



[Snliject, Mr. .I:iRt.ro\v.] 



fiO. 

 30. 

 15. 

 20. 

 10. 



In 1,125 experiments (subject, Mr. Peirce) — variations 15, :50, and BO gr.ain.s^tliere occurred confidence of '^, 3» 

 times (3 per cent.) : of 2, 102 times (9 per cent.) ; of 1, 282 times (25 per cent.): of 0, 700 times (03 per cent.). In 

 these experiments there were 332 (2!l per cent.) errors committed, of which 1 (0.3 per cent.) was made in connection 

 with a confidence 3; 10(3 per cent.) with a confidence 2; 51 (15 per cent.) with a confidence 1; 270 (81 per cent.) 

 with .a confidence 0. From which we find that in connection with a confidence of 3 tliere occurred I error in 35 cases 

 (3 per cent.): with a confidence of 2, 10 errors in 102 cases (10 per cent.); with a lonfidence of 1, 51 errors in 282 

 cases (ly per cent.) : with a confidence of 0, 270 errors in 700 cases (38 per cent.). 



, In 1,975 experiments (snliject, Mr. .lastrow) — variations 15, 30, and 00 gr.ams — there occurred confidence ol' 3, 02 



times (3 per cent.) ; of 2, U)0 times ( 10 per cent.) ; of 1, 594 times (:i0 per cent.) ; of 0, 1,123 times (.57 jjcr cent.). In 



• these experiments there were 451 (23 per cent.) errors committed, of which 2 (0.4 per cent.) were made in connection 

 with a confidence of 3; 12 (3 per cent.) with a confidence of 2; 97 (22 per cent.) with a confidence of 1, 340 (75 per 

 cent.) with a confidence of 0. Again, in connection with a confidence of 3, errors occurred twice in (ji cases (3 per 

 cent.) ; with a confidence of 2, 12 times in I'.Mi cases (C per cent.) ; with a confidence of 1, 97 times in .504 cases (10 per 

 cent.); with a confidence of 0, 340 times in 1,123 cases (30 per cent.). 



In 1.075 experiments (subject, Mr. .lastrow) — variations 5, 10, and 20 grams — there occurreil confidences of 3, 

 Miun' ; of 2, none ; of 1, 115 times (7 per cent.) ; of 0, l,.'i00 times (93 per cent.). In these experiments there were 5.38 

 (32 iier cent.) errors committed, of which 10 (3 i)er cent.) occurred in connection with a confidence of I : .522 (97 per 

 cent. ) with a confidence of 0. Ag.ain. in connection witli a confidence of 1, errors occurred 10 times in 115 cases (14 

 per cent.) : with a coulidence of 0, 522 times in 1,.5()0 cases (34 per cent.). 



Siiiind group. 



Ratio of weight.s. i Mark 0. ! Mark 1. Marl; 2. ' M.ark 3. 



1.015 \ ll'I'isl't 



I 00 wrong 



j 100 riglit 

 ( 35 wrong 



S 80 right 

 \ 8 wrong 



1.030. 

 1.060. 



