CHAPTEE 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 me- 

 chanical contrivances that we observe this to take place, 

 and the reason is very obvious. Such modes of ex- 

 pression originate with what are called practical men, 

 who, seldom having leisure or scientific education suffi- 

 cient to enable them to construct at once correct defini- 

 tions, 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, 



