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The Artificial Disturbances due to various Cars, Bycycles etc.
Various cars give influences of the great artificially disturbed magnetic fields on the magnetograph when they are passing through the vicinity of the magnetic observation-house. The amount of those influences are proportioned to the weights of cars. Disturbances in horizontal intensity are generally from twice to five-times as large as those in vertical intensity, and they change in proportion to the reciprocal cube of the distance from car to magnetograph. In the case of the distance of 10 meter from car, the amount of the influences are about 150 gamma for bus and truck (about 10 ton in weight),60 gamma for “sedan" and small truck or wagon (about 2 ton in weight),5 gamma for motor-bicycle, small motor cultivator and etc.(about 0.2 ton in weight) and 2 gamma for bicycle and etc.(about 0.02 ton in weight). The magnetizations of cars consist of the permanent magnetizations and the induced magnetization due to the earth magnetism, and the amounts of both magnetizations are nearly equal. The average magnetic moment of car is 5 × 104gauss as the weight of car being 300 kg. As the usual iron has nearly equal magnetization, it may be generally said that the substance of iron which make the magnetic field of 1 gamma at a distance of 1 meter is 30 grams.
But the magnetizations of motors, special measuring instruments and etc. are from twice to five-times larger than those of usual irons. Therefore, it is desirable that the iron, of which the intensity of magnetization is not yet measured, is kept apart from the observation house ten-times as far as the distance which are calculated from the magnetic moment of the car.
The magnetic observations at Kakioka, Memambetsu and Kanoya may be affected by artificially disturbed magnetic field, if a heavy car pass through the nearby road.
ln order to make the amount of this influence less than 0.5 gamma, the bus and the truck must be kept more than 70 meter apart from the observation house, the “sedan" and the small truck more than 50 meter, the other small car more than 25 meter.
If the magnetic observation house is built apart more than 30 meter from the building in which iron frames are not used, artificial fields doesn't need to be considered.
But if it is presumed that the cars frequent this building, it is desirable to be built apart 50 meter at least and 70 meter if it is possible.
When a building using a large quantity of iron materials is built, necessary separation should be estimated all on such occasions.
The special cars and the measuring instruments must be also held apart from observation house as far as the the neeessary distance to make their effect on the observation negligible. This problem is also investigated in this paper.
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