[ iv ] 
XXVII. On the reduction to a vacuum of Captain 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 William Ritchie, M.A. F.R.S., Rector of the Royal 
Academy of Tain 361 
Index 367 
Appendix. 
Presents received by the Royal Society, from 20 th November 1828, to 18 th 
June 1829. 
Meteorological Journal kept at the Apartments of the Royal Society, by order of 
the President and Council. 
I 
