CONTENTS. 
XI. On a new form of the differential thermometer, with some of 
its applications. By William Ritchie, A. M. Rector of 
Tain Academy. Communicated by J. F. W. Herschel, Esq. 
Sec. R. S. - - - - 129 
XII. On the structure and use of the suhmaxillary odoriferous gland 
in the genus Crocodilus, By Thomas Bell, Esq. F. L. S. G. S. 
Communicated by Sir Everard Home, Bart. V. P. R. S. 132 
XIII. 0 ?i the permeability of transparent screens of extreme tenuity 
by radiant heat. By William Ritchie, A. M. Rector of 
Tain Academy. Communicated by J. F. W. Herschel, Esq. 
Sec. R. S. - - - - 139 
XIV. On the derangements of certain transit instruments by the 
effects of temperature. By Robert Wood house, A. M. 
F. R. S. &c. _ _ _ _ 
XV. On some of the compounds of chromium. By Thomas 
Thomson, M. D. F. R. S. L. and E. Professor of Chemistry, 
Glasgow. - - - - 159 
XVI. Rules and principles for determining the dispersive ratio of 
glass; and for computing the radii of curvature for achromatic 
object-glasses, submitted to the test of experiment. By Peter 
Barlow, Esq. F.R. S. Mem. Imp. Ac. Petrop. &c. 231 
XVII. On the change in the plumage of some Hen-Pheasants. 
By William Yarrell, Esq. F. L. S. Communicated by 
William Morgan, Esq. F. R. S. - - 268 
