linked to periodicities discerned in records of such vari-
ables as rainhll. temperature, and winds. lnvariably,
however, the relation is weak. and commonly ofdubious
statistical significance.
Effects of solar variability over longer terms have also (15)
been sought. The absence of recorded sunspot activity in
the notes kept by European observers in the late seven-
teenth and early eighteenth centuries has led some schol-
ars to postulate a brief cessation of sunspot activity at
that time (a period called the Maunder minimum). The (20)
Maunder minimum has been linked to a span of unusual
cold in Europe extending from the sixteenth to the early
nineteenth centuries. The reality of the Maunder mini-
mum has yet to be established, however, especially since
the records that Chinese naked-eye observers of solar (25)
activity made at that time appear to contradict it. Scien-
tists have also sought evidence of long-term solar period-
icities by examining indirect climatological data, such as
fossil recoras of the thickness of ancient tree rings. These
studies, however, failed to link unequivocally terrestrial(30)
climate and the solar-activity cycle, or even to contirm
the cycle’s past existenue.
If consistPn! and re!iab!e geo!sgigal~-arek-xologieal
evidence tracing the solar-activity cycle in the distant
past could be found, it might also resolve an important(35)
issue in solar physics: how to model solar activity. Cur-
rently, chere are two models of solar activity. The tirst
supposes that the Sun’s internal motions (caused by
rotation and convection) interact with its large-scale
magnetic field to produce a dynamo. a device in which(40)
mechanical energy is converted into the energy of a mag-
netic field. ln short. the Sun’s large-scale magnetic field
is taken to be self-sustaining, so that the solar-activity
cycle it drives would be maintained with little overall
changc for perhaps billions of years. The alternative(45)
exp)anarion supposes that the Sun’s large-sca)e magnetic
field is a remnant of the field the Sun acquired when it
formed, and is not sustained against decay. In this
model. the solar mechanism dependent on the Sun’s
magnetiC field runs down more quickly. Thus, the char-(50)
acteristics of the solar-activity cycle uvuld be expected to
change over a long period of time. Modern solar obser-
vations span too short a time to reveal whether present
cyclical solar aCtivity is a long-lived feature of the Sun,
or merely a transient phenomenon.
17. The author focuses primarily on
(A) presenting two competing scientific theories concerning solar
activity and evaluating geological evidence often cited to support them
(B) giving a brief overview of some recent scientifrc developments
in s’olar physics and assessing their impact on future climatological research
(C) discussing the difficulties involved in linkinl: ter- restrial
phenomena with solar activity and indicating how resolving that issue
could have an impact on our understanding of solar physics
(D) pointing out the futility of a certain line of sci- entific inquiry
into the terrestrial effects of solar activity and recommendine ita
aban- donment in favor of purely physics-oriented research
(E) outlinine the specific reasons why a problem in solar physics has
not yet been solved and faulting the overly theoretical approach of modern
physicists.
18. Which of th.e following statements about the two models of solar
activity. as they are described in lines 37-55, is accurate?
(A) In both modgls cyclical solar activity is regarded as a long-lived
feature of the Sun, persisting with little change over billions of years.
(B) Tn both models the solar-activity cycle is hypothesized as being
dependent on the large-scale solar magnetic field.
(C) Tn one model the Sun’s magnetic fieid is thought to play a role in
causing solar activ- ity, whereas in the other model it is not.
(D) In one model solar activity is presumed to be unrelated to terrestrial
phenomena. whereas in the other model solar activity is thought to have
observable effects on the Earth.
(E) In one model cycles of solar activity with peri- odicities longer than
a few decades are con- sidered to be impossible, whereas in the other model
such cycles are predicted.
19. According to the passage, late seventeenth- and early eighteenth-century
Chinese records are impor- tant for which of the following reasons?
(A) They suggest that the data on which the Maunder minimum was predicated
were incorrect.
(B) They syggest that the Maunder minimum can- not be related to climate.
(C) Thcy suggest that the Maunder minimum might be \-’alid only for Europe.
(D) They establish the existence of a span of unusu- ally cold weather
worldwide at the time of the Maunder minimum.
(E) They establish that solar activity at the tirne of the Maunder minimum
did not significantly vary from its present pattern.
20. The author implies which of the followine about currently available
geological and archaeoloeical evidence concerning the solar-activity cycle?
(A) It best supports the model of solar activity described in lines 37-45.
(B) It best supports the model of solar activity described in lines 45-52.
(C) It is insufficient to confirtn either model of solar activity described
in the third paragraph.
(D) It contradicts both models of solar activity as they are presented in
the third paragraph.
(E) It disproves the theory that terrestrial weather and solar activitv are
linked in some way.
21. Tt can be inferred from the passage that the argu- ment in favor of the
model described in lines 37- 45 would be strengthened if which of the following
were found ta he tme?
(A) Episodes of intense volcanic eruptions in the distant past occurred in
cycles having very long periodicities.
(B) At the present time the global level of thunder- storm activity increases
and decreases in cycles with periodicities of approximately 11 years.
(C) In the distant past cyclical climatic changes had periodicities of longer
than 200 years.
(D) In the last century the length of the sunspot cycle has been known to
vary by as much as 2 years from its average periodicity of 11 years.
(E) Hundreds of millions of years ago, solar- activity cycles displayed the
same periodicities as do present-day solap-activity cycles.
22. lt can be inferred from the passage that Chinese observations of the Sun
during the late seventeenth and early eighteenth centuries
(A) are ambiguous because most sunspots cannot be seen with the naked eye
(B) probably were made under the same weather conditions as those made in Europe
(C) are more reliable than European observations . made during this period
(D) record some sunspot activity during this period
(E) have been employed by scientists seeking to argue that a change in solar
activity occurred during this period.
23. It can be inferred from the passage that studies attempting to use tree-ring
thickness to locate possi- ble links between solar periodicity and terrestrial
climate are based on which of the following assump- tions?
