CONTENTS. 
XVIII. Account of a Lithological Survey of Schehallien, made in 
order to determine the specific Gravity of the Rocks which com- 
pose that Mountain. By John Playfair, Esq. F. R. S. p. 347 
XIX. Observations and Experiments on Vision. By William 
Charles Wells, M. D. F. R. S. p. 379 
Presents received by the Royal Society, from November 1810 to 
July 1811, P -393 
Index. p. 399 
