PREFACE TO THE FIFTH VOLUME. 



The present Part completes the Fifth Volume, and with it 

 terminates the present Series of these Memoirs. This Volume 

 has extended to an unusual length, owing to the impossibility 

 of including in the four Numbers Professor Plateau's interesting 

 Researches on the Figures of Equilibrium, which, as the first 

 part had appeared in our Fourth Volume, it was desirable to 

 complete in the present Series. Besides the interesting re- 

 searches just alluded to, the present Volume contains, among 

 other valuable papers, Fresnel's celebrated treatise on Double 

 Refraction, Pliicker's various papers on Diamagnetism, Weber's 

 important memoir on the Measurement of Electro-dynamic 

 Forces, and Knoblauch's Investigations on Radiant Heat, which 

 have been pronounced by one of the most eminent philosophers 

 of this country as " not to be surpassed for extent and accuracy 

 of detail." 



The management will now pass into other hands, and the 

 work will receive that attention which of late I have been pre- 

 vented from devoting to it by increasing years and other circum- 

 stances. It is hoped, that by a more regular publication, and the 



