NATURAL HISTORY. 



53 



" The universal cause 



Acts to one end but acts by A .irious laws ; 

 Connects each being, greatest with the least ; 

 Made beast in aid of man, and man of beast." POPE. 



a table, or on the palm of the hand, a marble, or any other small globular body, and 

 crossing it alternately with the fore and middle fingers 

 so disposed that the marble shall touch only the outer 

 edges or surfaces of the two fingers, the person will 

 believe that he touches two marbles, although he knows 

 that only one is present. The explanation of this 

 illusion is as follows : The mind refers, involuntarily, 

 all sensations experienced at different parts of the body 

 to the position in which such parts are usually placed. 

 Now the cross-ing of the fingers does not prevent us 

 feeling either of them in contact with the marble, as if 

 they were placed naturally side by side. But in the 

 habitual position of the fingers side by side, it is impos- 

 sible that the outer edges of any two fingers can be at 

 the same time placed in sufficient contact with a single 

 marble or other similar rounded body ; and thus when such contact actually 

 takes place simultaneously, by the contrivance of crossing the fingers, then 

 the mind involuntarily believes the thing to be impossible, takes it for granted 

 that two marbles, not one, must be present ; and hence arises the sensation and 

 perception of two distinct bodies. 



CHAPTER V. 



CLASSIFICATION OF THE VARIOUS ANIMALS. 



161. WJiy are animals arranged by naturalists into classes, 

 orders, sub-orders, families, &c. ? 



Classification prevents the necessity of frequently and fully 

 describing any animal referral to ; it ensures correct identity in 

 the observations and communications of naturalists. It also 

 answers as a sort of dictionary wherein, from the properties of 

 things, we proceed to discover their names, thus forming the 

 inverse of ordinary dictionaries, where the names direct us to the 

 properties. But no arrangement of animals can be perfect ; first, 

 because we may not be acquainted with all the species ; secondly, 

 because of some of the species we may know very little ; and, 

 thirdly, because of those which we knifcv best, the greater part are 

 known as more or less domesticated; and, further, because the 



