This paper has for its object to propose, refering chiefly to the model experimental studies of surface and totally immersed crafts, a new idea that probably enables us to presume the total resistance of a body by only measuring the total resistances of two models in arbitrary different scales, without any necessities to use the absolute values special to the body and the models except some special cases. Principal detailed investigations are made upon the items such as (a), when each model has the surface condition equal to that of the original and (b), when each model has the surface condition different from that of the original.

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A full description on a new type of the harmonic analyser devised by the auther is given with an actual result of analysing an isosceles-triangular wave. So called "Henrici's Principle", shown by the following expression, makes the mechanical construction of a harmonic analyser simple. Let y=f(θ), then the two Fourier's coefficients of the nth harmonics can be transformed by integration by parts as follows. [numerical formula] In each of the above expressions, the term in the brackets being zero, it is only necessary to make the mechanical integration of the last term which consists of 2 elements instead of 3 in the left-hand one. This principle has already been adopted in many types of harmonic analysers in use with various processes. This new type is so constructed as to give the value of the integral by relative motion between a horizontal plane and an integrating roller of the same type as those of an ordinary polar-planimeter, the plane being movable in the direction of y-axis and the shaft of the integrating roller revolvable in a horizontal plane by a train of friction rollers. This instrument is applicable for any wave length from 0.5cm. to 140cm., and for any wave height under 60cm., nevertheless, the instrument has a small size of 10cm×20cm×35cm. The order of harmonics which can ersily be analysed by this instrument varies as the fundamental wave length, and is shown in the following. Fundamental wave length 5 10 20 50 100 140cm, Order of harmonics to the 10 15 20 25 30 35th

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