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Proceedings of the Royal Society 
Fellows whom we have lost; or those of our late eminent Honorary 
Fellows, Schonbein and Foucault. A full biography, however, of 
our late President, Sir David Brewster, will appear ere long from 
some well-qualified pen, and one of Professor Walker-Arnott by 
Dr Cleghorn. 
The following Gentlemen were elected Foreign Honorary 
Fellows of the Society : — 
Gustav Robert Kirchhoff, Professor of Physics in the University of 
Heidelberg. 
Rudolph Virchow, Professor of Pathological Anatomy in the University 
of Berlin. 
Monday , 21 st December 1868. 
The following Communications were read : — 
1. On the Colour of Aerial Blue. By Sir George Harvey. 
This paper is intended to prove that the colour of blue in the 
sky and in the landscape is simply the result, in the former, of the 
darkness of space, as seen through the white light contained in the 
atmosphere ; and, in the latter, of the same cause as shown in the 
dark and distant portions of the landscape being viewed through 
the interposed medium of air filled with white light. The colour 
of aerial blue being due in both cases to the same cause, namely — 
a dark body neutralised as to its darkness by being seen through a 
white and transparent medium. 
2, On the flotation of a Bigid Body about a Fixed Point. 
By Professor Tait. 
{Abstract). 
This paper contains an attempt to exhibit the mutual relations of 
some of the more important of the various processes which have 
been employed in solving one of the most celebrated problems of 
Dynamics. The Quaternion analysis has been throughout used, as 
far more briefly comprehensive and more suggestively expressive 
than the ordinary Cartesian analysis. 
A brief sketch of the kinematical relations of the problem is first 
