39 
Dr. Joule described a peculiar kind of mirage which he 
had witnessed from the northern extremity of Douglas Bay, 
Isle of Man, and at an elevation of 20 feet above the surface 
of the water. At about 9 a.m. a number of chimneys in the 
town were fired, and the products of combustion were driven 
out to sea by a very gentle breeze. Presently the wind 
changed and drove the smoke at right angles to its former 
track. The steamer for Liverpool had in the meantime 
attained a distance of about three miles, and, although some- 
what obscured, was distinctly visible through the smoke. 
Noticing something extraordinary in her appearance, he 
viewed her through a telescope, and then observed that 
nearly the whole of the hull was obscured by the horizon, the 
uppermost part of the paddle-boxes, the bowsprit, and tafferel 
being alone visible, whilst at the same time the masts and 
funnel appeared. considerably elongated. Quarter of an hour 
afterwards, when the smoke had cleared away and the steamer 
was about seven miles distant, the hull was seen as usual, 
quite unobscured by the horizon. Dr. Joule attributed the 
phenomenon to a stratum of highly refractive gases, lying 
about 20 feet above the level of the sea and gradually diluted 
and diminished in extent on its upper and lower sides, so as 
to produce the effect of a convex lens. 
Dr. Angus Smith said : I saw once a very remarkable 
instance of the diversion of the rays of light from the straight 
line. Although fogs are common on our hills, I have met no 
instance of similar exaggeration of effect among us. I went 
with some friends up Skiddaw, and near the top entered a 
cloud which prevented us from seeing many yards before us, 
although it was not extremely dark. When moving over 
those loose stones which form a highway to the summit for 
a considerable distance, we observed a building which 
appeared to us about fourteen feet high. The side towards us 
seemed to be a wall nearly square, and we took it for granted 
that the top of the hill was attained and that the foremost 
