9 questions/ 13 minutes
The mid-thirteenth-century King's Mirror contains extraordinarily
accurate descriptions of sea mammals and other natural phenomena.
The section dealing with the North Atlantic describes only three
phenomena that assume an aspect of the marvelous: the hafgerdingar (sea
fences) and the Norse merman, both sighted in the Greenland Sea,
and the hafgufa, sighted in Icelandic seas. Scientists
have long assumed that the Norse mermen were nothing more than
manatees or dugongs; however, that theory ought surely to be reconsidered
in light of new research findings indicating that hafgerdingar are
a visual effect created by anomalous atmospheric refraction of
Light is refracted downward during a temperature inversion, a condition in
which atmospheric temperature increases with elevation. During an inversion,
irregularities in the atmospheric temperature profile, especially thermoclines
(layers where the temperature gradient is steeper than in adjacent layers),
create irregularities in light refraction. The resulting optical distortion
may be so severe as to make ordinary objects unrecognizable, even at short
distances. One excellent source for mermen images, for instance, may have
been whales projecting their heads vertically out of the water. (Such activity,
called "spy-hopping" is common among cetaceans.) Our computer simulations
suggest that, with changes in the temperature profile, a whale's head can
appear slender and vertically elongated to a degree three times its actual
height above water. Since the horizontal dimension remains unchanged, the
distorted image possesses a large height-to width ratio, a form associated
with humans. The refractive distortion diminishes if the image can be viewed
from above the thermocline, but to sail thirteenth-century vessels, Norse
mariners worked from the deck, only a few meters above the sea. Subsequent
use of higher-decked ships and of elevated lockouts would explain the infrequent
sightings of mermen by Norse mariners in later centuries.
Apparently, the thermoclines that generate mermen images are most likely
to be created when a warm air mass moves slowly over significantly cooler
surface air, as in the last stages of a warm front, when the warm-cold interface
has descended almost to the surface. (Some experimental verification of this
hypothesis has already been provided by Wegener, who correlated mirages in
the North Atlantic with the arrival of warm fronts.) The typical conditions
just before a major storm in the Greenland Sea, dead calm followed by a sudden
rise in temperature, are ideally suited to the development of thermoclines.
The amount of optical distortion depends directly on the temperature difference
between the two air masses, which in turn determines the strength of the
front and the severity of subsequent storms. The King's Mirror quite correctly
associated the appearance of Norse mermen with the advent of storms on the
open sea. However, Norse mariners thought that the mermen brought on the
storms. In fact, the opposite was true.
1. Which of the following statements best
expresses the central idea of the passage?
(A) Early Norse mariners were incorrect in attributing to mermen
the power to bring on storms at sea.
(B) A Norse merman is actually a distorted visual image created by anomalous
(C) The Norse merman is unlikely to be merely a manatee or a dugong.
(D) The thermoclines that generate mermen images are more common in the North
Atlantic than elsewhere in the world.
(E) A whale projecting its head vertically out of the water is an excellent
source for mermen images.
2. The author is impressed by the King's
Mirror because of its:
(D) faithfulness to reality.
(E) sound reasoning.
3. According to the passage, the thermoclines
that generate mermen images are most likely to be present when two
air masses in close proximity differ significantly in:
(D) rate of movement.
(E) moisture content.
4. According to the passage, an object
sighted at sea will appear most distorted by a thermocline when the:
(A) distance from the object to the observer is short.
(B) vertical dimension of the object is large.
(C) surface of the water near the observer is smooth.
(D) elevation of the observer above the water level is low.
(E) frontal system that created the thermocline is strong.
5. According to the author, Norse mariners
made which of the following errors?
(A) They worked their ships only from the deck.
(B) They converted to higher-decked ships in later centuries.
(C) They did not record their sightings of mermen in later centuries.
(D) They mistook one sea mammal for another.
(E) They mistook an effect of storm conditions for a cause of storms.
6. Which of the following phrases could
best be substituted for the word "reconsidered" in the last sentence
of the first paragraph, without changing the meaning of the passage
as a whole?
(A) evaluated objectively
(B) verified experimentally
(C) questioned seriously
(D) compared with other theories
(E) reasserted more emphatically
7. According to the passage, the likelihood
of optical distortion is increased in the presence of which of the
following atmospheric conditions?
I. a temperature inversion
II. a warm front
III. dead calm followed by a sudden rise in temperature
(A) I only
(B) II only
(C) I and III only
(D) II and III only
(E) I, II, and III
8. Which of the following would most strengthen
the author's assertions concerning the cause of mermen images?
(A) accurate measurement of the average temperature gradient
in a thermocline
(B) empirical verification of computer simulations made by the author
(C) explanation by historians of the reasons behind the design changes made
in Norse ships after the thirteenth century
(D) discovery of records showing frequent sightings of mermen by Norse mariners
after the thirteenth century
(E) discovery of errors in the correlations developed by Wegener
9. The passage implies that the hafgerdingar are
most likely to be seen as a result of which of the following?
(A) irregularities in the atmospheric temperature profile
(B) movement of a cool air mass over significantly warmer surface air
(C) upward refraction of light rays through the atmosphere
(D) a period of several consecutive warm days on the Greenland Sea
(E) a change in atmospheric temperature profile after a storm at sea