On the Errors of our Sensations. 259 



The discrepancy between 26 and 28 is not greater than may 

 be expected from the smallness of some of the observed quan- 

 tities. These numbers agree very well with those given by 

 Meyer for his first two sorts of hard steel, which, I gather, 

 were in better condition than the others (Wiedemann's An- 

 nalen, xviii. p. 245). The values that agree best with each 

 other are about 



k = 2'l, //, = 4tt£ = 26-4 



to 



£ = 2-5, /*= 31-4. 



I propose to give some details in a future paper. 



The result is, that if the magnetic induction in a permanent 

 magnet be supposed to arise from a permanent magnetomotive 

 force acting on a magnetic resistance, the resistance can be 

 determined by the behaviour of the magnet on separation ; 

 and this resistance is numerically identical with that offered 

 to external magnetomotive force. 



XXXIX. On the Errors of our Sensations: a Contribution to 

 the Study of Illusion and Hallucination* . By Emile Yung, 

 D.ScA 



WHILE investigating, during the last few years, the 

 question of animal magnetism, I have been 'led to pay 

 some attention to the phenomena of illusion and hallucination. 

 We know in a general way to how many errors our sense- 

 organs are exposed ; it is useful to ascertain these in one's 

 self, to produce them in other people, and to try to correct 

 them in every body; and it is necessary to determine them for 

 each sense and for each individual. The same phenomenon is 

 often appreciated in very different manners by different ob- 

 servers, or by the same observer at different periods. We 

 should always adopt it as an absolute rule to observe the same 

 fact several times under different subjective conditions before 

 asserting its objective existence. And if it is desirable that 

 this rule should be applied by well qualified observers, it ought, 



* The present memoir gives only the commencement of a series of ex- 

 periments undertaken upon the normal human subject with the purpose of 

 checking and measuring the value of the testimony of our organs of sense. 

 Dr. Yung begs that physicists and naturalists will have the goodness to 

 communicate to him any isolated but positive observations that they may 

 possess upon this subject. 



t Translated from the Bibliotheque Univeisette, Archives des Sciences 

 Physiques et Naturelles, ser. 3, tome ix. p. 156. 



