PREFACE. Vll 



With regard to the figures, we have thought it quite 

 proper to represent an original specimen, which is 

 apt to give a more perfect idea than geometrical out- 

 lines alone j but, to make them more perfectly un- 

 derstood, have annexed magnified and geometrical 

 figures, as thinking them more valuable for being 

 original j as copies of works, however good, are 

 surely not to be preferred ; especially as, by seeing what 

 is done before us, we are able to manage the subject 

 better, seeing more properly how to show it in a 

 better position, or correct the mistakes. 



Very common subjects will be included, as they are 

 often more essential to the farmer, builder, mecha- 

 nic, etc., and are generally least known to minera- 

 logists : indeed, we mean to leave no stone unturned, 

 to make the work as universally useful as possible. 



We beg our friends to accept our grateful thanks 

 for the assistance we have received in this arduous un- 

 dertaking, promising them to be ever attentive to their 

 kindnesses, as a work of this universality requires 

 many helping hands. 



