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There are three typical forms of globoid worms and their wheels, they are : (1) Hindley worms, (2) helical gears and their enveloping worms, (3) plane toothed wheels and their enveloping worms. The surfaces of contact of these worms and wheels can be analyzed mathematically. In this way, with some assumed data we can get their contour lines, and thus it can be said : (1) Concerning to a Hindley worm and its wheel, their surface of contact is formed of two surfaces, the one is a plane which passes the axis of worm and perpendicular to the axis of wheel, and the other is a curved surface which is very resemble to the above mentioned plane and intersects it. The surface of each wheel tooth has two contact lines on the approach side, but on the recess side there is only one. Thus the tooth bearing on this wheel tooth cannot be said good. (2), (3) As for a toothed wheel and its enveloping worm, the surface of contact is in nearly tangential to the circumference of worm surface. The tooth bearing on a wheel tooth is in their center portion, and in good condition. Now we consider the manufacturing process of these wheels and worms. The Hindley worm can be cut by single tools, but cannot be ground by grinding wheels. Its wheel must be cut by specially made hobs, and also cannot be ground. On the contrary, the plane toothed wheel and its enveloping worm can be easily cut by a milling cutter and ground by a grinding wheel of simple form. In constructing these wheels and worms, the Hindley worm and its wheel must be built with very strictly limited allowance, but the plane toothed wheel and its enveloping worm can be built somehow under less restrictions.

The teeth of gears which are planes and their enveloping worms can be cut or ground by milling cutters or grinding wheels of simple forms. When the plane teeth of wheels are inclined properly to the wheel axes, the tooth-bearings on wheel teeth may be at the central portion of them. And the angles between axes of wheels and worms are selected properly, then the tooth-bearings may be made very wide. The teeth of wheels may be made in cylindrical or conical surfaces. The tooth-bearings on the wheel teeth may be improved, if the surfaces are properly selected. When the teeth are concave conical, tooth-bearings will be the best, and when they are of circular arc form, they will be fairly good.

Industrial fatigue was examined by means of flicker-test and subjective fatigue test in a certain factory of heavy electric appliance.According to the results obtained, conveyer system generally causes more intensive fatigue than the other type of working system when unskilled workers are involved.The present results will be followed up by the same method of observation after the workers acquire more skill in the conveyer system.