[ iv ] 



XXVII. On the reduction to a vacuum of Cdi^imn Kater's convertible pendulum. 

 By Captain Edward Sabine, of the Royal Artillery, Secretary to the 

 Royal Society 331 



XXVIII. On the geometrical representation of the powers of quantities, whose 

 indices involve the square roots of negative quantities. By the Rev. John 

 Warren, M.A. late Fellow and Tutor of Jesus College, Cambridge. 

 Communicated by the President 339 



XXIX. An experimental examination of the electric and chemical theories of 

 galvanism. By V^^illiam Ritchie, M.A. F.R.S., Rector of the Royal 

 Academy of Tain 361 



Index 367 



Appendix. 



Presents received by the Royal Society, from 20th November 1828, to I8th 

 June 1829. 



Meteorological Jom-nal kept at the Apartments of the Royal Society, by order of 

 the President and Council. 



