OBSERVATION AND DESCRIPTION. 185 



would have been ill grounded ; I should have ascribed those 

 sensations to a wrong cause. 



Innumerable instances might be given, and analysed in 

 the same manner, of what are vulgarly called errors of sense. 

 There are none of them properly errors of sense; they are 

 erroneous inferences from sense. When I look at a candle 

 through a multiplying glass, I see what seems a dozen candles 

 instead of one : and if the real circumstances of the case were 

 skilfully disguised, I might suppose that there were really that 

 number ; there would be what is called an optical deception. 

 In the kaleidoscope there really is that deception : when I 

 look through the instrument, instead of what is actually there, 

 namely a casual arrangement of coloured fragments, the ap 

 pearance presented is that of the same combination several 

 times repeated in symmetrical arrangement round a point. 

 The delusion is of course effected by giving me the same sen 

 sations which I should have had if such a symmetrical combi 

 nation had really been presented to me. If I cross two of my 

 fingers, and bring any small object, a marble for instance, into 

 contact with both, at points not usually touched simultaneously 

 by one object, I can hardly, if my eyes are shut, help believing 

 that there are two marbles instead of one. But it is not my 

 touch in this case, nor my sight in the other, which is de 

 ceived ; the deception, whether durable or only momentary, is 

 in my judgment. From my senses I have only the sensations, 

 and those are genuine. Being accustomed to have those or 

 similar sensations when, and only when, a certain arrangement 

 of outward objects is present to my organs, I have the habit 

 of instantly, when I experience the sensations, inferring the 

 existence of that state of outward things. This habit has 

 become so powerful, that the inference, performed with the 

 speed and certainty of an instinct, is confounded with intuitive 

 perceptions. When it is correct, I am unconscious that it 

 ever needed proof; even when I know it to be incorrect, I 

 cannot without considerable effort abstain from making it. 

 In order to be aware that it is not made by instinct but by 

 an acquired habit, I am obliged to reflect on the slow process 

 through which I learnt to judge by the eye of many things 



