Marvels of the Universe 791 
are much hotter and lighter than the air somewhat higher up. Rays of light from an object enter- 
ing the rarefied layers of air obliquely downwards are bent up more and more by refraction the further 
they penetrate, and at last fall on a stratum at an angle greater than the critical angle. This they 
cannot penetrate, but total reflection takes place and the rays reach the observer’s eye with changed 
direction, seeming as if they came from a point as far below the reflecting stratum as the object 
itself is above it, whilst it often happens that the latter is itself seen directly by rays which have 
not passed down into the reflecting layer. Thus an appearance is presented like that of an object and 
image reflected in a lake of calm water. 
Such a Mirage is sometimes seen across lakes on calm autumn mornings. Here it is the water 
that heats the lower layers of air. In Arctic regions, Scoresby and others have related that images 
of ships have sometimes been seen 7m inverted positions in the air at a time when the ships them- 
selves were too far off to be directly seen. Scoresby once recognized his father’s ship by seeing its 
inverted image through a telescope when the object itself was over thirty miles off. In such cases 
the ice and sea cool the lower atmospheric strata so that their density rapidly increases downwards. 
Rays passing obliquely upwards into the rarer layers are bent more and more downwards (owing to 
differences of density), till they suffer total reflection, and their images appear in the air as far above 
as the objects themselves are below the horizon. 
Allied to these appearances is the phenomenon known as looming. Distant objects are seen 
abnormally elevated above their true position, and appear especially near, sometimes in an erect 
position, sometimes inverted. It is recorded that on one occasion the top of Etna “‘ appeared by 
refraction like an island in the sea.” Several ships sailed from Malta to take possession of this 
supposed new island, but soon the image vanished, and the quest was seen to be in vain (Archibald), 
A necessary condition for the production of such phenomena is that the air should be at rest, 
and then, if for any reason, as by undue heating or undue cooling, the regular rate of decrease of 
temperature upwards is disturbed, total reflection at the surface of a rarer stratum will occur. The 
rays of light passing through the air will be gradually deflected in direction and then bent down 
or wp, towards the side on which the denser strata le, thus often affording a view of objects which 
would not otherwise be seen. What is seen over heated land is a portion of the sky apparently on 
[Bu Theo. Carreras. 
MIRAGE OF BREAKERS ON THE BARRIER REEF. 
After a phenomenon instanced by the late W. Saville Kent, when the invisible breakers beating on the further shore of the 
lagoon were clearly visible reflected in the sky above. 
