TEANSLATOR'S PREFACE. 



In bringing this Translation of Helmholtz's Popular 

 Scientific Lectures before the public, I have to thank 

 Mr. A. J. Ellis for having placed at the disposal of the 

 Publishers the translation of the third Lecture ; and also 

 Dr. Francis, the Editor of the ' Philosophical Magazine,' 

 for giving me permission to use the translation of the 

 fifth Lecture, which originally appeared in that Journal. 

 In addition to the Editorial charge of the book, my 

 own task has been limited to the translation of two of 

 the Lectures. I shoidd have hesitated to undertake the 

 work, had I not from the outset been able to rely upon 

 the aid of several gentlemen whose names are appended 

 to the Contents. One advantage gained from this division 

 of labour is, that the publication of the work has been 

 accelerated ; but a far more important benefit has been 

 secured to it, in the co-operation of translators who have 

 brought to the execution of their task special knowledge 

 of their respective subjects. 



E. ATKINSON. 



Staff College: 

 March 1873. 



