The characteristics of ACE High Sensitive Hygrometer at low temperature below 0°C were measured with following results. This hygrometer of electric resistance type, having been developed by Prof. K. Shiba of Tokyo Universicty and having very small measuring elements (6. 0 × 3. 0 mm² × 0.2 mm) made from the pith of some plant, is quite available for measuring and remote-recording humidity distribution, especially a diffusion layer, and has excellent characteristics at usual temperature above 0°C in current use.
1) The hysteresis effect of the testing elements was not observed at -15°C. In the experiments, instantaneous change in humidity was made by using four vessels of a different constant humidity and the final humidity was about 65 % R.H. At such a humidity ehe hysteresis effect would be most prominent if it would exist.
2) As to the time lag characteristics : -
i) Wind effect (winth the velocity 0, 0. 5, 6 m/s, at, -20°C, making instantaneous change of about 20% R.H.) : The time constant at 0, 0.5, 6 m/s is 390, 200, 135 sec respecpectively for hydrating process and 540, 310, 220 sec respectively for dehydrating process.
ii) Temperature effect (winth the temperature 20, 0, -10, -20°C at the wind velocity 3 m/s, making instantaneous change of about 20% R.H.) : The time constant at 20, 0, -10, -20°C is 6, 20, 50, 140 sec respectively for hydrating process, and 25, 70, 130, 230 sec respectively for dehydrating process.
iii) The time lag characteristics of ACE Hygrometer at every temperature both above and below 0°C were found to be about 7 times better compared with those of Honeywell Hygrometer which is the best one of electric resistance type in current use.
3) According to the comparative test of the humidty elements of a different dimension, it would be possible to gain more excellent characteristics by decreasing the dimension, especially the thickness of the humidity element.
4) The diffusinong coefficient was determined from the data of gradient of water vapour pressure above the surface of ice by employing ACE Hygrometer in the low temperature room and the rate of evaporation of water from the surface of ice measured by means of the “dialguage method” measuring a decrease of the thickness. The value obtained was about 0.2 cm²/s at -17°C and the range of the diffiusion layer was found to be about 0.5 cm above the surface of ice.

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A snow scale for measuring the maximum depth of accumulated snow in remote regions was developed.
The snow scale consists of a wooden pole with 10 cm aluminium pins of 3 mm in diameter driven into the pole at 10 cm intervals on both sides of the pole. The pin is bent downward by the settling force of snow when it is covered with new snow of about 10 cm in depth, but is not bent by snow or ice accretion. The snow scale is set up before the snowfall and after the snow melts the maximum snow depth can be seen from the height of the bent pins.
Good agreement between the depth measured by this snow scale snd that obtained by actural measurements in various places of the country, was seen. The tests were run over the past 5 years.

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