vi PREFACE TO THE SIXTH EDITION. 



I have read all with care. I have added a few 

 paragraphs here and there to the Essays ; the other 

 papers I have not altered, farther than by correcting 

 some mere verbal errors, and, in two or three instances, 

 incorporating with the text, paragraphs printed at the 

 time as footnotes. 



I have prefixed the dates and names of the volumes 

 in which they were published ; and though in their 

 present arrangement I have not adhered strictly to 

 chronological order, I have done so as far as is consis- 

 tent with papers on the same subjects following each 

 other. 



I have entitled them ' Experimental Investigations/ 

 to avoid confusion with the better title, appropriated 

 by Faraday, of ' Experimental Researches.' 



Towards the end I have given a few observations 

 of little value in themselves, but made on phenomena 

 of rare occurrence. While this edition was going 

 through the press Sir C. Wheatstone has called my 

 attention to a book entitled ' Elemens de Physique 

 Gen^rale, par Jules Guyot, Paris, 183 2,' in which, though 

 the style of argument is a priori and somewhat dog- 

 matic, the author attributes natural phenomena to 

 motion either of translation, as he terms it, or molecular, 

 and attacks the theories of fluids, ethers, &c. It is a 

 work of considerable merit, and shows, when conjoined 

 with the references I have given, that many minds are 

 independently converging to the same theory, the which 

 I believe will ultimately prevail. 



