PURPOSE: To prepare isobaric lines by stacking two sheets of glass one on the other, and placing weights on the respective centers of an anticyclone and a cyclone, and illuminating the sheets of glass from above using a sodium lamp, and drawing a weather map using interference fringes between the two sheets of glass.

CONSTITUTION: Sheets 2, 2' of glass are stacked on a map 1 drawn by white lines on a black background. The sheets of glass are illuminated by a sodium lamp 3 from above. When some weights 4, 4' are placed on the map 1 in such a manner that the center of an anticyclone and that of a cyclone correspond to the respective weights 4, 4', the upper sheet 2 of glass is distorted and a slight change in the space between the sheets of glass is caused. Since the sheets of glass are illuminated by the sodium lamp 3 of single-colored light from above, interference fringes 5 of light are formed at intervals corresponding to pressure. A precise weather map can thus be drawn by setting the weights 4, 4' with accuracy. Besides, the fringes would not cross each other on account of the nature of the interference fringes.