608 Messrs. Aichi and Tanakadate: Theory of 
of (1) and (41) increases by 7%. But at the same time for (II), 
the difference between the maximum and the minimum yalues 
is diminished by another factor F’. ? 
(e) The above is more manifestly shown in the case of the 
laboratory experiment with a cylindrical glass rod and a 
straight slit as a source of light. The stationary points of 
(II) at which the maximum value coincides with the minimum 
are easily found by 
K®=m x interval of the maximum and minimum of (1), 
where m represents an integer. 
(f) According to Airy’s theory, the law of distribution of 
the colours of the rainbow is independent of the magnitude 
of the drop. But in the case of the finite source, the colour 
distributions are changed by the magnitude of the drop, 
especially in the supernumerary bows. 
(g) The supernumerary bows almost lose the colour as the 
consequence of the finiteness of the source. This effect is 
more remarkable when the drop becomes larger. 
10. To show the above-mentioned results, we repeated 
rough experiments with glass rods and a straight slit as a 
source of light. 
Using homogeneous light, we see that when the slit is very 
narrow Airy’s theory holds good, and that when the breadth 
of the slit is increased, the positions of bows (or fringes in 
this case) change very little. As another effect of the increase 
of the breadth of the slit, the bows become indistinct, especially 
in the supernumerary bows. This effect is remarkable when 
the diameter of the rod is large. We could not observe the 
turning point, at which the maxima and minima interchange, 
as the difference of the intensities is very small. But we can 
roughly say that the point at which the bows become almost 
indistinguishable corresponds to the position at which the 
breadth of the bow coincides with that of the slit. 
Again, using white light, it is easy to see that the colours 
of the supernumerary bows change when the magnitude of the 
rod is changed, and that the supernumerary bows almost lose 
the colour and become indistinct when the breadth of the slit 
is Increased. . 
Finally, we have to thank Prof. Nagaoka for suggesting 
the problem and giving kind advice during the course of the 
investigation. 
