CONTENTS. 
XVII. Memoir on the occurrence of Iodine and Bromine in certain Mineral 
Waters of South Britain. By Charles Daubeny, M.D. F.R.S. Pro- 
fessor of Chemistry in the University of Oxford page 223 
XVIII. Experiments to determine the difference in the Number of Vibrations 
made by an Invariable Pendulum in the Royal Observatories of Green- 
wich and Altona. By Captain Edward Sabine of the Royal Artillery , 
Secretary to the Royal Society 239 
XIX. Experiments to ascertain the Correction for V ariations of Temperature, 
within the limits of the natural temperature of the Climate of the South 
of England, of the Invariable Pendulum recently employed by British 
Observers. By Captain Edward Sabine of the Royal Artillery, Secre- 
tary to the Royal Society 251 
XX. On a new Register-Pyrometer, for measuring the Expansions of Solids, and 
determining the higher Degrees of Temperature upon the common thermo- 
metric scale. By J. Frederic Daniell, Esq. F.R.S 257 
XXI. On the Phenomena and Laws of Elliptic Polarization, as exhibited in the 
Action of Metals upon Light. By David Brewster, LL.D. F.R.S. 
Lond. 8$ Edin 287 
XXII. Researches in Physical Astronomy. By John William Lubbock, Esq. 
Fellow of the Royal Society. 327 
XXIII. On the Error in Standards of Linear Measure, arising from the thick- 
ness of the bar on which they are traced. By Captain Henry Kater, 
P.P. and Treasurer of the Royal Society 359 
