, on April 16, 1871|thumb|left Looming is the most noticeable and most often observed of these refraction phenomena. It is an abnormally large refraction of the object that increases the apparent elevation of the distant objects and sometimes allows an observer to see objects that are located below the horizon under normal conditions. One of the most famous looming observations was made by
William Latham in 1798, who wrote:
Thomas Jefferson noted the phenomenon of looming in his book
Notes on the State of Virginia: He was unable to explain this phenomenon and did not think refraction could account from the perceived changes of shape of the object in question. Other famous observations that were called "mirages" may actually be referring to looming. One of those was described in
Scientific American on August 25, 1894, as "a remarkable mirage seen by the citizens of
Buffalo, New York". Such looming—sometimes with apparent magnification of opposite shores—have been reported over the
Great Lakes. Canadian shorelines have been observed from
Rochester, New York, across
Lake Ontario, and from
Cleveland across
Lake Erie. The landforms over distant, normally beyond the horizon, were sometimes perceived as away. Looming is most commonly seen in the
polar regions. Looming was sometimes responsible for the errors made by polar explorers; for example,
Charles Wilkes charted the coast of
Antarctica, where later only water was found. The larger the size of the sphere (the planet where an observer is located) the less curved the horizon is.
William Jackson Humphreys' calculations showed that an observer may be able to see all the way around a planet of sufficient size and with sufficient
atmospheric density gradient. ==Sinking==