The Tropics, namely the zone between the Tropic of Cancer and the Tropic of Capricorn was named the Torrid Zone in the past on the basis of solar climate. However, neither the Tropic of Cancer nor the Tropic of Capricorn are boundaries of a temperature zone defined by a specific isotherm. From the standpoint of solar climate, the Tropic of Cancer as well as the Tropic of Capricorn should be the most basic climatic boundaries, as Louis (1958) and Lauer and Frankenberg (1988) maintained and presented climatic maps of the world. It was geographer Supan (1879) and climatologist Köppen (1884) who defined the Tropics as a temperature zone characterized by a mean temperature of 20°C or above for the coldest month. Therefore, the boundary of this temperature zone, “the Tropics”, should correspond with the 20°C isotherm of the monthly mean temperature of the coldest month. It may be assumed that the above mentioned two scholars adopted this critical value, considering the relationship between distribution of tropical plants and of temperature in the coldest month, although they did not state this distinctly. Since then, this value has often been cited to delimit the Tropics. In the year 1918, Köppen wrote a famous paper on the classification of climates on the basis of temperature, precipitation and annual trend, and in substance, however, on the basis of the relationship between the distribution of plants and climates of the world. This epochmaking paper played an important role in pioneering the field of climatology. In that paper he defined the Tropics as a temperature zone with mean monthly temperature of the coldest month of 18°C or above. Since then, regarding the classification of climates, numerous results have been published, on the basis of the so-called effective method. They may be classified into two groups : climatic systems initiated by Köppen (1918), Köppen and Geiger (1928), de Martonne (1909), Gorczynski (1935, 1942), Trewartha (1954, 1968), and Miller (1959), for example, belong to the former, and those which were initiated by Philippson (1921), v. Wissmann (1939, 1948, 1962), Blair (1949), Creutzburg (1950, 1964), Troll (1955), Troll and Paffen (1964), for instance, to the latter. Climate systems initiated by these two groups differ. Köppen et al. divided climates into humid, arid and cold climates, and the humid climates into, for instance, tropical, (subtropical), temperate and polar. In this way, the tropical climates, defined by a critical value of mean monthly temperature of the coldest month (for instance, 18°C or above, or an approximate critical value) set bounds to the humid tropics alone. Therefore, according to this climatic system, arid tropical region should inevitably be outside the Tropics. According to the latter climatic system, climates were divided into, for instance, tropical, subtropical temperate, boreal and subpolar-polar zones, on the basis of the specific isotherms, and then, except subpolar-polar climates, they are divided into climate types on the basis of, for instance, the annual trend of humidity (or aridity). Therefore, according to this climatic system, the tropical zone was defined on the basis, of, for instance, either the suitable isotherms, the absolute frost limit, or the line on which diurnal and annual range of temperature are equal. Accordingly, the tropical climatic region covers the humid as well as the dry tropical climates. It was v. Wissmann (1948) who delimited the warm tropics of the world on the basis of absolute frost limit, and moreover, in his climatic system (v. Wissmann, 1962) defined warm-, temperate-, cool-, and cold tropics, analysing the vertical structure of climatic regionality of the tropical highlands and mountains.
One of the most interesting paleontological contributions to general knowledge is evidence that once-dominant giant reptiles died out in the end of the Cretaceous period. Recently, on the basis of the iridium enrichment in Cretaceous-Tertiary (K-T) boundary layers, the Berkeley research group suggested that the process of mass extinction of species is extraterrestrial in origin, probably caused by the impact of large meteorites on the Earth. Since this suggestion, it has become fashionable for geochemists to discover an iridium abundance at K-T boundary sites or at other mass-extinction horizons around the world. Many Earth- and planet-scientists have eagerly discussed on the possibilities of a global catastrophe due to bolide impacts. The probability of striking the Earth by an Earth-crossing asteroid is estimated to be not no small. As a matter of fact, in January 18, 1991, astronomical observations found a small asteroid crossing the Earth's orbit within half the distance to the Moon. Earth-crossing comets are even more plentiful. The probability of comet collisions to the Earth is supposed to increase extremely when the Solar System encounters with a dense molecular cloud in the Galaxy. Some volcanologists protest against the impact hypothesis, insisting that a bolide impact is not the only way to cause a global catastrophe. Despite that a large-scale volcanic eruption can produce iridium enrichments, the presence of shock quartz at K-T boundary sites remains a problem for proponents of volcanism. It seems that the extraterrestrial-origin hypothesis has advantage over the volcanic hypothesis. Various hypotheses of mass extinction are reviewed in the first half of this paper. It is a well-known fact that the Earth's magnetic field has repeatedly flip-flopped. The great circulation of molten iron in the Earth' core generates the geomagnetic field. The sophisticated theory of electromagnetic fluid dynamics explains the mechanism of the geomagnetic generation, but there still remain uncertainties in the mechanism of geomagnetic reversal. Some paleomagneticians speculated that the asteroid impact is an immediate cause of geomagnetic reversal, but others rejected the idea of such a linkage from standpoints of microtektite studies. Recently, a Japanese research group has analyzed samples of sedimentary rock, whose sedimentation rate was 3 m/ka during the Matuyama-Brunhes reversal period, and discovered changes in both oxygen and carbon isotope ratios coincident with reversal. The decrease in carbon isotope ratio of 1 permill corresponds supposedly to the 40 % reduction of biomass, which indicates a large amount of CO2 gas flows into the ocean and the atmosphere from the biosphere. The concurrent decrease in oxygen isotope ratio can be explained as the CO2-induced greenhouse effect. The coincidence of a biomass changes with a geomagnetic reversal implies that the reversal may be one of possible causes of mass extinction. The biosphere is protected by the shield effect of magnetic field against solar high-energy particles. During the time of reversal when the shield effect disappears, the biosphere may be directly exposed to harmful ultraviolet ray and further affected by the concurrently-occurred global climate change. On the basis of observational facts that the geomagnetic dipole moment has been rapidly decreasing, many geomagneticians give a warning that the Earth is now standing at the starting point of a magnetic reversal. If the decrease will continue as it is, the geomagnetic field will completely disappear in one thousand years or later.
The Takanosu Basin is located in the northern part of the Dewa Hills, the inner zone of the Northeastern Japan Arc, and filled with a series of deposits in which the Yuguruma Formation takes the uppermost part. The Yuguruma Formation is composed mainly of lacustrine blueish gray tuffaceous silt and contains intercalated gravel, sand, acid tuff, and lignite layers. Its total thickness is estimated to beabout 200 meters or more. Significant tectonic deformation of the formation is not recognizable. Paleomagnetic measurements indicate that the Yuguruma Formation is Middle Pleistocene in age, and its deposition finished a little later than 0.35 Ma. There are three higher terrace surfaces in the Takanosu Basin, i.e., the T-H1, T-H2, and T-H3 surfaces. The T-H1 surface provides the depositional surface of the Yuguruma Formation. The T-H1, T-H2, and T-H3 are indirectly dated as ca. 0.35-0.44 Ma, ca. 0.20 Ma, and ca. 0.16-0.19 Ma respectively, on the basis of accumulation rate of weathered tephra which covers the surfaces and intercalates dated Late Pleistocene marker-tephra layers. The presence of the higher terraces underlain by the thick sediments indicates a change in tectonism from subsidence since early Pliocene time (the end of Funakawa age) to uplift all over the basin in Middle Pleistocene time, because the Yuguruma Formation emerged and the T-Hl surface was formed around 0.35 Ma. The tectonic development of the besin has still continued to deformed the T-H3 surface and Late Pleistocene T-Lla surface.
Hanseison was established as an administrative village in the early Tokugawa period. Up to date, most of them can be seen as basic regional units in rural Japan. It is impossible to understand a present rural society without reconstructing formation processes of the territorial organization in the rural area through the Tokugawa period. In the changing processes of productive activities and social relations, rural space has been differentiated as well as integrated. Though the sub-systems have been formed in the rural space through these processes, the rural space has been structured as one territory by internal or external forces. From the above viewpoint, the author has attempted to clalify the structurization of the rural space where the spheres of cultivation and the social groups were formed, and to investigate the territorial unity of the hanseison. The field for the case study is a hanseison Ono, in Sibata county of Rikuzen province, situated in a small basin where the river terrace is formed. The territory of this hanseison contained several settlements, and could be divided into two difierent life spaces, Ono and Komatsukura. The changing processes of the rural space and the territorial unity of the hanseison through the Tokugawa period are divided into the following three stages, and their situations are also summarized. 1. The first stage (ca. 1580-1650) : It seems that the peasants who settled down sporadically in the medival ages reclaimed fields near their own yashiki (homestead) each peasant had independently established his narrow sphere of cultivation. But, at the beginning of the 17 th century, mainly in the south-western part of this area, the wastelands were largely reclaimed. These cultivated lands were owned by the peasants residing in different areas of the village. The integration of the rural space through the land tenure form was arising. The territory of hanseison was formally fixed by Kan'eiKenchi (the land survey) in 1642 as the unit for domination. In that time, however, it was the extended sphere of productive activities that contributed to the structurization of the rural space. In this stage, internal unity was remarkable. Then the feudal clan conformed this structured space as a unit for domination. 2. The second stage (ca. 1650-1750) : Both population and the number of honbyakusho (independent farmers) increased rapidly, and several settlements emerged, and machi grew as a central place. But, little expansion was made in the cultivated space, and sphere of cultivation were differentiated. At the same time, the formation of the territorial groups was promoted. Several goningumi (neiborhood groups) differentiated the rural space, but on the other hand, they were integrated under the administrative system. Furthermore, two groups of the supporters which belonged separately to two temples were formed. In this stage, the rural space was structured by the system of the social groups organized for administrative aim by feudal clan. Then, the territorial unity of the hanseison had been strengthened by external political power which had controlled the farmers through its territoriality. 3. The third stage (ca. 1750-1870) : Because of the severe famines, the number of honbyakusho decreased rapidly. Residential space also decreased, but four settlements remained. Goningumi lost its function, and kumi, the territorial groups coinciding with four settlements, strengthened the character as an organization for mutual aid, and differentiated the rural space. These groups were integrated into the territory of the hanseison, however, each settlement took a part of its function.
Numajiri Bokusen was born in 1775 and died in 1856 in Tsuchiura (the present Tsuchiura City, Ibaraki Prefecture). He was adopted into the family of doctor Numajiri Sekigyu in the same town. He studied drawing, penmanship, astronomy and geography. Later, he ran and taught at a private elementary school (terakoya). Among his products, his most important achievements were in the geographical field. He constructed an epochal terrestrial globe from wood, bamboo and Japanese paper in 1855. It is alleged that he actually investigated it in 1800, but had hidden it after a warning from his neighboring friend who was a samurai (warrior and servant) of the Tsuchiura-Han (feudal clan). In 1855 he finally decided to produce and distributed his globes to various parts of the country. Some of them have been found in the possession of old families in several places. They are made by using the technology to frame Japanese umbrellas, which does not require the use of nails. Each globe is folded up in a similar manner to a coarse oil-paper umbrella. This is significantly advantageous compared with others during that period. Later his globe was called the “Kasasiki-chikyugi” (umbrella-like globe). While his globe is famous in Japan, research data on it are insufficient. Therefore, the author examined it and measured the size of each part. This could not be done perfectly because the measurement could only be done when the globe was unfolded. However, much information was obtained. This paper describes the form of the globe with its size and some details of the history of its preservation. The shapes of the shorelines on the globe were evidently renewed. Therefore, it is confirmed that the map was scheduled to be engraved as a woodcut based on the latest information available at the time. Since similar portable globes were produced in other countries, the author will examine the relationships between them.