Mr H. Blackadder on Unusual Atmospherical Refraction. 67 
The accompanying sketches of appearances in PI. II. exhibited 
by it in the month of April (which is the least favourable season), 
were taken at the time of observation, and may serve to give some 
idea of what may be seen in this neighbourhood. The place of 
observation was the sea-shore ; and the objects represented" are 
those which bounded the horizon at the mouth of the Frith of 
Forth, including part of the coasts of Fife and East Lothian. 
With the assistance of a good telescope, the rigging of the ves- 
sels, &c. would have been much more distinctly observed, but 
that, unfortunately, was not at hand ; and it was not wished to 
represent any thing that Avas not distinctly seen by the naked 
eye, or with the assistance of a small pocket telescope. The 
phenomenon commenced about 3 p. m. and remained visible to 
about sunset. The atmosphere was very serene. There were 
but few clouds, not dense, in the western hemisphere, and at a 
considerable height. Towards the zenith, the blue of the sky 
was pale, becoming of a faint brassy colour, as it approached 
the verge of the eastern horizon. The objects farthest off, that 
is to say, the Isle of May, and the vessels, were from SO to 30 
miles distant ; and there the lower atmosphere was equally calm, 
as indicated by the small progress made by the ships, and the 
crowded, state of their sails. Sometimes the images were very 
distinct, and remained stationary for a considerable time, when 
the particular shapes and colour of the rocks of the Isle of May 
could be distinguished as in a transparent painting. But, du- 
ring the most part of the time, the images were continually 
changing their form and elevation ; and, at times, with a motion 
resembling that of the aurora borealis. During the whole period 
that the appearance lasted, there was a distinctly marked hori- 
zontal line in the atmosphere, extending across the Frith, from 
the most distant visible point of the coast of Fife to that of East 
Lothian ; and which was probably the boundary of two strata of 
air of very different density. The elevation of this line was al- 
most constantly varying, and the appearance of the images va- 
ried accordingly. Sometimes it was lowered near to the horizon, 
at other times elevated several degrees above it, and most fre- 
quently simultaneously, and in its whole extent. In proportion 
as this horizontal line was lowered, that portion of the atmo- 
sphere which occupied the space between it and the sea, be- 
e 2 
