CONTENTS. 
XII. Observations of a Comet , made with a View to investigate 
its Magnitude and the Nature of its Illumination. To which 
is added , an Account of a new Irregularity lately perceived in 
the apparent Figure of the Planet Saturn. By William Hers- 
chel, L. L. D. F. R. S. - - p. 145 
XIII. Hydraulic Investigations, subservient to an intended Croo- 
nian Lecture on the Motion of the Blood. By Thomas 
Young, M. D. For.Sec.R.S. - p 164 
XIV. A Letter on the Alterations that have taken place in the 
Structure of Rocks, on the Surface of the basaltic Country in the 
Counties of Derry and Antrim. Addressed to Humphry 
Davy, Esq. Sec. R. S. By William Richardson, D. D. 
p. 187 
XV. A Letter on the Differences in the Structure of Calculi , which 
arise from their being formed in different Parts of the urinary 
Passages ; and on the Effects that are produced on them, by the 
internal Use of solvent Medicines, from Mr. William Brande, 
to Everard Home, Esq. F. R. S. - - p. 223 
XVI. Some Observations on Mr. Branded Paper on Calculi. 
By Everard Home, Esq. F. R. S. - p. 244 
XVII. On the Changes produced in Atmospheric Air, and Oxygen 
Gas, by Respiration. By W. Allen, Esq. F. R. S. and W. 
H. Pepys, Esq. F.R.S. - - - p. 249 
