162 



ON THE EXTERNAL SENSES 



the top of St. Paul's, has returned home through the air in a straight line, in 

 four or five hours. 



Buffon asserts, that a hawk or eagle can travel two hundred leagues in ten 

 hours, and relates a story of one that travelled two hundred and fifty leagues 

 in sixteen hours. 



A Newfoundland dog has in like manner been brought from Plymouth to 

 London by water, and having got loose, has run home by land with a speed 

 so rapid as to prove that his course must have been nearly in a straight line, 

 though every inch of it was unknown to him. 



At such instances we start back, and, as far as we can, we disbelieve them, 

 and think we become wise in proportion as we become skeptical. Meanwhile, 

 nature pursues her wonder-working course, equally uninfluenced by our doubts 

 or our convictions.* 



Even among mankind, however, we occasionally meet with a sort of sen- 

 sation altogether as wonderful and inexplicable. For there are some persons 

 so peculiarly affected by the presence of a particular object, that is neither 

 seen, smelt, tasted, heard, or touched, as not only to be conscious of its pre- 

 sence, but to be in an agony till it is removed. The vicinity of a cat not un- 

 frequently produces such an effect ; and I have been a witness to the most 

 decisive proofs of this in several instances. It is possible that the anomalous 

 sense may in this instance result from a peculiar irritability in some of the 

 nervous branches of the organ of smell, which may render them capable of 

 being irritated in a new and peculiar manner : but the persons thus affected 

 are no more conscious of an excitement in this organ of sense than in any 

 other ; and from the originality of the sensation itself find no terms in any 

 language by v/hich the sensation can be expressed. 



Sharks and rays are generally supposed by naturalists to be endov/ed with 

 a peculiar sense in the organ of a tubular structure found immediately under 

 the integuments of the head though they have not agreed as to the exact 

 character of this additional sense. Trevannius calls it generally a sixth 

 organ of sensation. M. Jacobson, and Dr. de Blainville, who quotes his 

 authority, regard it as a local organ of touch. M. Roux, who seems to have 

 examined it with great attention, believes it to be the source of a feeling of a 

 middle nature between the two senses of touch and hearing-! The bat appears 

 to have, in like manner, an additional sensific power, for it is observed to 

 avoid external objects when in their vicinity, while the eye, ear, and nose are 

 closed, and there is no direct touch : and this peculiar feeling has been called 

 a sixth sense generally by naturalists, without discriminating it farther. 



What is the cause of those peculiar sensations which we denominate hun- 

 ger and thirst 1 A thousand theories have been advanced to account for 

 them, but all have proved equally unsatisfactory, and have died one after an- 

 other almost as soon as they have received a birth. We trace indeed the 

 organs in which they immediately reside, and know by the sensations them- 

 selves that the one exists in the region of the stomach, and the other in that 

 of the throat : but though we call them sensations, they have neither of them 

 any of the common characters of touch, taste, hearing, seeing, or smelling. 



* The fact of the migratory power of one kind of animals confirms the fact of the migratory power of 

 others. While the question was confined to birds it was too often denied by many naturalists, merely 

 from the difficulty of accounting for it ; and it was said, in opposition to Catesby and White, and all our 

 best ornithologists, that our summer birds only disappear by creeping into holes and crevices to hibernate. 

 And hence, even so late as 1823, the late Dr. Jenner felt himself called upon to examine such assertions 

 with a view of disproving them; which he has done in one of the most agreeable essays on the natural 

 history of migratory birds to be found in our own or any other language. " A little reflection," says be, 

 " must compel us to confess that they are endowed with discriminating powers totally unknown to, and 

 for ever unattainable by, man. I have no objection to admit the possibility that birds may be overtaken by 

 the cold of winter, and thus be thrown into the situation of other animals which remain torpid at that 

 season ; though I must own I never witnessed the fact, nor could I ever obtain evidence on the subject that 

 •was to me satisfactory ; but, as it has been often asserted, may I be allowed to suppose that some deception 

 might have been practised with the design of misleading those to whom it might seem to have appeared 

 obvious 1" Phil. Trans. 1824, p. 11. The strongest argument against all such disbelief, arising from the 

 difficulty of accounting fbr the migration of birds, is to turn to the migration of fishes, and to the parallel 

 cases of remote travel in other animals, which are given above. The respective marvels give support to 

 each other, till disbelief itself becomes at length.the greatest marvel of the whole. 

 , t See farther on this subject, Edino. Journ. of Science, No. iii. Art. iii. p. 87, 1825. 



