INTUODUCTION. 63 



ntctcd withit. Ail animals, man excepted, have it: it is 

 altogether uuallied to any principle of intelligence in 

 the human mind; and is totally distinct from the five 

 outward senses common to both man and inferior ani- 

 mals. Neither is memory at all concerned in it : it is 

 purely instinctive, and is therefore seldom found to 

 err ; and, being instinctive, it is very universally dis- 

 tributed. This sixth sense is that whereby a dog, re- 

 moved to a distance, is enabled to return alone, although 

 the intervening portions of the distance are utterly un- 

 known to him, and that, in such return, it is evident he 

 can neither be assisted by seeing, hearing, smelling, or 

 recollection. 



whether of the sixth sense noticed by Dr. Roget, or of that of the 

 judgment of distances, or of some other, he is not able to decide. 



With regard to the perception of external objects " without vision" 

 (I would rather say without apparent light) or contact, there are 

 other ways of accounting for this property without the intervention 

 of a sixth sense. When we know that a condur (vultur gryphus, 

 Lin.) can either see or smell, and perhaps both, a carcass, one or 

 tAvo miles distant, we can readily conceive that the eye in nocturnal 

 and crepuscular animals may be so exquisitely susceptible, as to be 

 stimulated by rays of light infinitely finer than our organs can perceive. 

 This perception might also be accounted for by the acuteness of 

 smelling, which we know is, in some animals, so great, that the ap- 

 proach of many objects is ascertained by it without vision. Another 

 mode by which the situation of objects is perceived without seeing 

 or coming in contact with them, is by means of the ears: this prin- 

 cipally relates to large objects. It is not difficult to accustom one- 

 self to walk by the side of a wall or along a dark passage, so as 

 neither to touch the wall nor swerve from the centre of the passage. 

 The sonorous rays reverberated (even the breathing may effect this) 

 from the objects, and again striking the ear, may enable it to judge 

 of the distance by the acuteness of the sound, or the length of its 

 return. This perception of large objects, without seeing or contact, 

 1 have often witnessed. 



