vi PREFACE TO 



The list of contributors will show to whom \ve are indebted for the 

 technical articles which distinguish this Dictionary ; and the articles 

 themselves will give evidence of their having been treated, in all cases, 

 by men who are thoroughly experienced in the processes which they 

 have described. When the initial letters at the end of the articles do 

 not indicate the authors of them, I am directly responsible for them. 

 In a work treating of the useful applications of Science, it became 

 necessary to introduce such portions of those sciences, which have 

 been economically useful to man, as would render the processes 

 described sufficiently intelligible to all readers, and show the aid 

 which has been rendered by scientific enquiry. Therefore, several 

 divisions of Physics, Chemistry, Geology, and Mineralogy, are suc- 

 cinctly dealt with. Of Chemistry, it should be remarked, that the 

 very rapid advances of discovery in that science, have involved a 

 revolution in the mode of viewing the constitution of bodies, and 

 necessitated the construction of a new mode of expressing that 

 constitution. During the transition period, there naturally arises 

 much difficulty in determining with exactness the formula} which 

 shall correctly express the composition of a compound. This natural 

 difficulty has been aggravated by the unfortunate introduction of 

 hypothetical views respecting the constitution of compounds, and the 

 creation of systems of notation which are constantly liable to some- 

 what capricious alteration. As this Dictionary is for the use of a 

 public which cannot be expected to be acquainted with each change 

 in the views entertained by the different schools of Chemistry, it has 

 been thought desirable to retain the formula) with which they have 

 been long familiar, and to give in another (black) type the formula) 

 which have been adopted by most modern chemists. 



It will be observed that in some cases the Imports and Exports of 

 productions used in the Arts or Manufactures, which were given in the 

 former Editions, do not appear in the present one. This arises from 

 the impossibility of obtaining them : the Custom House authorities 

 now entering a large number of articles under the head of ' Unenume- 

 rated,' which were formerly given in detail. This is much to be 

 regretted, since it removes the power of tracing the progress of the 

 special use, or industry, to which the article in question belongs. 



To all those gentlemen who have favoured mo with contributions my 

 best thanks are due. I have, however, to express my obligations more 

 especially to Mr. HIGGIN, whose article on 'Calico Printing' gives a 

 more satisfactory description of that industry than any other to be 



