VI PREFACE. 



Ill pursuance of this plan, the alterations from 

 the original " School of Arts," and also the ad- 

 ditions to it, became so considerable, that the work 

 has assumed nearly the appearance of a new pro- 

 duction j and some apology is perhaps due for 

 altering the features of Iniison's book so far, that it 

 is no longer rccognizeabie. In this form it has 

 passed through several editions, a circumstance 

 that induces the hope, that the labour of the 

 present editor has not been altogether useless. 



In a book intended to exhibit only the popular 

 elements of science, it would be in vain to expect 

 much original matter. To draw from authentic 

 sources, and to arrange and describe with clear- 

 ness and precision the principal known facts, ap- 

 pears to be all that the nature of the undertaking 

 admits of. The following work, therefore, is de- 

 rived from the discoveries of others ; but it will be 

 found upon perusal, that in several instances, 

 where the editor's profession or opportunities of 

 observation enabled him to add any thing to the 

 stock of particular knowledge, he has not failed to 

 make the attempt. 



With respect to the present edition, he has 

 merely to notice, that a considerable part of it has 

 been re-written ; the whole has been revised ; and 

 every endeavour has been made to render it a 

 source of entertainment and instruction to those 

 who have not the opportunity of consulting more 

 detailed treatises 021 the several subjects which are 

 here considered. 



T. W. 



