PREFACE TO THE FOURTH VOLUME. 
ON the publication of the Sixteenth Part of the Scientific 
Memoirs, completing the Fourth Volume, I may remark, as the 
progress of the work has been slower than before, that I have 
of late been left to my own means for its continuation, as since 
1841 it has no longer received support from the British Associa- 
tion. I trust, however, that although the Parts have appeared 
at longer intervals, their contents will be found quite equal in 
interest and importance to those of the preceding volumes. 
Keeping in view the object of the work, as designed to assist 
in elucidating the subjects of inquiry which from time to time 
engage the attention of men of science in our own country, the 
present Volume includes a series of Memoirs on the Heat and 
Elasticity of Gases and Vapours, by Holtzmann, Magnus, and 
Regnault ; whilst on subjects connected with the Theory of 
Light and Colours, will be found those of Wartmann, Neu- 
mann, Seebeck, and especially that of Biot on Polarized Light, 
which of itself is a work of considerable extent. 
For the Memoirs of MM. Plateau, Wartmann and Doye, I 
am indebted to the authors, who kindly communicated them to 
me. I have also to acknowledge the valuable assistance which 
I have received during the progress of the Volume from Pro- 
fessors Faraday, Challis, Graham, Lloyd, W. H. Miller, Wheat- 
