Abstract
It is very important to determine directly the sense of rotation of various diagrams such as dynamic characteristics, Lissajous' figures, etc. appearing on the fluorescent screen of the Braun tube oscillograph. But so far there seemed to have been no such direct method as far as the writer is aware, and the sense of rotation has usually been infered from the properties of observed phenomena. The writer has recently tried a stroboscopic method which would render some service in the study of this line.
The necessary additional implement is a thin metallic disc revolved with a suitable motor which was, in the writer's exoeritnent, an induction motor connected to the same source as that of the diagram. The disc has some small holes equidistant along the circumference of a concentric circle.
If the diagram on the fluorescent screen is looked at along an imaginary line fixed in space through the holes of the revolving disc, the fluorescent spot may be seen to move in the same sense or opposite to the rotation of the diagram, according to the frequency of the diagram, the speed of the disc and the number of holes. If the number of holes be made equal to that of pairs of poles of the induction motor, the spot always seems to rotate in the same sense as the diagram.
The writer has made several experiments to verify this method. By aid of the results of the experiments, he confirmed that the method is applicable to the diagram of low and moderate frequencies.
