168 Proceedings of the Royal Society of Edinburgh. [Sess. 
This mirage appears to be a daily affair in sunny weather, not an elusive 
phantom but a robust phenomenon. 
So far as I can gather from the literature of the subject, some of the 
features seem to be novel. As I have had, owing to what I might describe 
as the permanency of the phenomenon on this road, possibly unusual 
opportunities of observing it, may I be permitted to refer specially to a 
few of these ? 
Lying down on the road and looking along its surface, one sees a long 
stretch of the road apparently reflecting figures with their colours. One 
sees black and silvery emanations from the surface of the road when 
the mirage is seen, some of these distinctly local. The bituminous surface 
of this road, when parts are taken off and examined under the microscope, 
is covered with small particles of sand or quartz which show brilliantly 
in sunshine. 
That the lighter of these particles are rising into the air where mirage 
is visible, I have proved by pulling a small sledge over the road, having 
rough cardboard coated with gum placed about 1 1 inch above the road 
surface, and getting upon it a deposit of the crystals. 
The part that bitumen plays in this example of the phenomenon is, I 
think, to absorb and retain the solar heat (the phenomenon persists when 
the sun is temporarily obscured by clouds), and the convection currents carry 
up the brilliant particles which, with those embedded, I think constitute the 
silvery band referred to. 
{Issued separately September 26, 1918.) 
