ILLUSIONS OF THE SENSES. 533 



triloquism ; the deceptive appearances of the 

 mirage of the desert, the looming of the hori- 

 zon at sea, the Fata Morgana of the coast of^ 

 Calabria, the gigantic spectre of the Brocken in 

 the Hartz, the suspended images of concave 

 mirrors, the visions of the phantasmagoria, the 

 symmetrical reduplications of objects in the 

 field of the kaleidoscope, and a multitude of 

 other results of the simple combinations of the 

 laws of optics. 



The second class comprehends those in which 

 the cause of deception is more internal, and 

 consists in the peculiar condition of the nervous 

 surface receiving the impressions. Ocular spec- 

 tra of various kinds, impressions on the tongue 

 and the eye from galvanism, and those which 

 occasion singing in the ears, arising generally 

 from an excited circulation, are among the 

 many perceptions which rank under this head. 



The third class of fallacies comprehends those 

 which are essentially mental in their origin, and 

 are the consequences of errors in our reasoning 

 powers. Some of these have already been 

 pointed out with regard to the perceptions of 

 vision and of hearing, the formation of which is 

 regulated by the laws of the association of ideas. 

 But even the sense of touch, which has been 

 generally regarded as the least liable to fallacy, 

 is not exempt from this source of error, as is 

 proved by the well known experiment of feeling 



