CONTENTS. 
XIX. Consideration of the objections raised against the geometrical representa- 
tion of the square roots of negative quantities. By the Rev. John 
Warren, 31. A. of Jesus College, Cambridge. Communicated by Thomas 
Young, 31. D. Foreign Secretary to the Royal Society. . . page 241 
XX. Anatomical description of the foot of a Chinese female. By Bransby 
Blake Cooper, Esq., Surgeon to Guys Hospital. Communicated by 
Peter Mark Roget, 3I.D., Secretary to the Royal Society. . . 255 
XXI. Some observations on the functions of the nervous system , and the relation 
which they bear to the other vital functions. By Alexander Philip 
Wilson Philip, 31. 1). F.R.S. L. 8$ E 261 
XXII. On the respiration of birds. By William Allen and William Hasle- 
dine Pepys, Esqrs. Fellows of the Royal Society 279 
XXIII. On the spontaneous purification of Thames water'. By John Bostock, 
31.D. F.R.S. 8§c 287 
XXIV. On the composition of chloride of barium. By Dr. Edward Turner, 
Professor of Chemistry in the University of London. Communicated by 
Dr. Dionysius Lardner, Fellow of the Royal Society 291 
XXV. On a new series of periodical colours produced by the grooved surfaces 
of metallic and transparent bodies. By David Brewster, L.L.D. F.R.S. 
L. 8s E 301 
XXVI. On the Nerves of the Face ; being a second paper on that subject. By 
Charles Bell, Esq. Fellow of the Royal Society 317 
