CHAPTER I. 



GENERAL PRINCIPLES. 



THERE is scarcely anything of more frequent occurrence 

 than the transition from an incorrect mode of expres- 

 sion to a popular error ; we see instances of this daily 

 occurring. No doubt the incorrect mode of expression 

 usually arises, in the first instance, either from con- 

 fusion of ideas or false appreciation of facts, or both 

 taken together ; but when once brought into currency, 

 it is frequently accepted not only as a fitting designa- 

 tion, but actually as a true explanation of the nature or 

 mode of operation of the thing designated, and thus 

 grows into what is called a popular error. 



It is more especially in matters connected with 

 mechanical contrivances that we observe this to take 

 place and the reason is very obvious. Such modes of 

 expression originate with what are called practical men, 

 who, seldom having leisure or scientific education suffi- 

 cient to enable them to construct at once correct defi- 

 nitions, commonly judge by the eye or the touch, and 

 translate the evidence of one of these senses into a 

 name. It is in this way that the peculiar languages of 

 handicrafts usually grow up, and the apprenticeship to 

 these consists to a great extent in the acquisition of the 

 proper application of such technical terms; so that, 



