A hexagonal plate simulated snow particle is exposed to an airflow containing water droplets in a vertical wind tunnel. The motion of the droplet around the plate is determined by stereoscopic analysis in order to find the trajectory grazing the model. The collection efficiency thus obtained is most similar to that of sphere in Langmuir and Blodgett's results but our value seems to be larger than all of their collection efficiency and to have finite value in the region of K≤1/12 where Langmuir and Blodgett's collection efficiency of sphere becomes zero.

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In the tracer experiment of elevated-source diffusion, sometimes there are found two peak values in the vertical concentration profile, which means two centerline-heights of concentration. One corresponds to the tracer release height and the other, the lower-level one, seems to correspond to the lower neutral or near-neutral layer. The vertical spread of concentration in the lower layer is larger than that in the upper layer. In this circumstance the surface concentration near the source is mostly determined by the diffusion from the lower-level centerline height of plume, namely the extraordinarily high surface concentration is expected to occur near the source, which cannot be explained in the light of customary knowledge of elevated-source diffusion.

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Comparing the crustal section obtained from seismic-refraction measurements off Hidaka, Hokkaido, with those obtain ed off Northeast. Honshu, and considering the structural features in and around Hokkaido, the continental crustal layer in the western half of Ho k kaido is inferred to be an extension of that of the Honshu arc. T he thick 4.2 km/sec layer found off Shizunai is considered to be compose d of the depositional materials of the Yezo geosyncline of the Cretaceou s time. The structural contrast between this sedimentary fu rrow and the Hidaka mountain range, where the continental crustal la y er seems to be shallow in depth, suggests a large-scale thrust of the crust of eastern Hokkaido upon that of western Hokkaido. Th is structural trend can be traced from the southern end of Hokka ido to the northern part of the Tatary strait. it is suggested t hat this thrust and vast sedimentation in the foredeep on its western side a re the products of the Hidaka orogenesis, and the structural bounda r y between them marks a plate boundary in the Mesozoic e ra. The extension of this plate boundary, which separates the Okhotsk pl a te from the Eurasian plate, is pursued along the Northern trough and further eastward between the Kolyma and Koryak mountain rang e s. The tectonic movements of the Okhotsk plate in the Mesoz oic to Palaeogene time are estimated in relation to the Hidaka orogenesis. Many phenomena such as the igneous activity along the m argin of the Asian continent in Late Mesozoic, the geographical distributions of the so-called Green Tuff region and of the present heat flow values in Hokkaido, and the shallow seismic activity in Sakhalin can be explained by this hypothesis.

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The stratified wind tunnel in which the density of air gradually changes with height is available for experimental studies on thermal convective air currents under the developed thermal inversion layer. The convective currents do not thrust through the upper light layer, but spread out horizontally, and the circulation pattern is similar to that of the so-called heat island obtained by numerical simulation. It suggests the mechanism of the local flow patterns of urban heated and urban polluted air.

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The cosmic ray intensity variations on August 1-10,1972, recorded by large ionization chamber are presented, and the characteristics of the variations are briefly described.

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Concentrations of thorium isotopes 232Th,230Th and "sTh were determined in the river water collected at ten main rivers in Japan. The concentration of dissolved 232Th in river water was one order of magnitude higher than that in the Pacific surface waters. The weighted averages were 2.7x 10-8 g/l for 232Th and 2.8x 10-13 g/l for ""Th. The constancy in 232Th and 230Th concentration with time was observed, but the concentration of 228Th in river water was quite variable. Accordingly,228T h/232Th activity ratio showed a wide range of variation from 37 to 0.65 during the period of study.

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Content of plutonium in the water of eight main rivers in Japan was determined. The average value of the total content of plutonium is 1.4x10-3pCi/l in which 0.4x 10-3 pCi/1 is contained in the suspended matter. The annual run-off plutonium is only 0.12% of the accumulated plutonium on land. This suggests that the fallout plutonium is adsorbed on soil surface firmly and it is difficult to be leached out.

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The steady-state or Lagrangian type formulation of one-dimensional models of an isolated cumulus cloud has been used by Simpson et al. (1969), Weinstein (1970) and other researchers in order to investigate the effect of the physical processes of clouds on the dynamical development of convective motions.

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Some special considerations should be necessary for the method. of measurement of very low concentrations, such as the global background values of submicron aerosols. We have added some improvements to a Pollak-type condensation nucleus counter for this purpose (Figs.1-3). Though the Pollak-type counter is very practical for daily observation, it is not sufficient for the purpose of the long-term comparison of data, because it is, as is well known, a relative instrument. Therefore it is necessary to have another instrument of an absolute counting type, such as an Aitken-type condensation nucleus counter. A photographic recording Aitken-type counter has been developed for the purpose (Figs.4-6).

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By the application of the refraction law to the readings of P and S times at Morioka (MOR), Miyako (MIY) and Ofunato (OFU), in northern Honshu, for deep earthquakes that occurred in Hokkaido and the Sea of Okhotsk, the seismic wave velocities in the "deep earthquake zone" (high-V, high-Q zone) are estimated.
The seismic waves of relatively shallow earthquakes occurring in this zone travel from their origins to the above stations over the deep earthquake zone alone. However, waves from origins deeper than a certain depth refract on their way in the "low-V, low-Q region" that exists just beneath the deep earthquake zone (Fig.7). This low-V, low-Q region is also characterized by high-a, as was suggested by Utsu (1969) from the analysis of the values of Vp/Vs. The observed values of Vp/Vs may suggest that the waves passed through the low-V, low-Q region or not.
For the present data, the values of Vp/Vs for earthquakes deeper than about 300 km are somewhat larger than those for earthquakes shallower than that depth (Fig.8). This suggests that the waves from earthquakes deeper than about 300 km may have travelled on the way in the low-V, low-Q region beneath the deep earthquake zone. Then, only those data that are shallower than about 300 km are available for estimating the velocity.
In order to strip off the upp e rmost layer of 50 km thickness, the travel times of P and 5, and values of dT/dA for an origin of 50 km depth are obtained from earthquakes of about 50 km depth which occurred off the east coast of northeastern Honshu (Fig.9). On reference to the observed values of dT/di, the data on the surface of the earth are converted to those at the surface of a depth of 50 km.
In the calculation of the velocity, a layered structure is assumed and the velocity in a layer of depths from 50 km to 100 km, v1, is given properly. In the first place, the average velocities for layers from 100 km to the depths of the earthquakes are estimated from the converted A and T for respective shocks of depths of 114 km and 132 km. Next, by applying Bullen's relation, v=A exp (-kh), to the value of v1 and estimated velocities, v, the value of k for the layer from 50 km to 130 km is estimated, and the velocity at a depth of 115 km is adopted as the average one in the layer from 100 km to 130 km.
By the same procedure, average velocities for layers of depths from 130 km to 160 km and from 160 km to 220 km are estimated from earthquakes occurring in these layers. Finally, Bullen's relation is applied once again to all values of v.
Velocities with depth in the deep earthquake zone, larger by about 2-6% than those by Jeffreys-Bullen or Honda, and Sagisaka and Takehana, were obtained and shown in Fig.12, where the values given of v1 are 8.05 km/sec and 4.63 km/sec for P and S waves, respectively.

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