6 8S TL. Moreland—Formation of Diffraction Bands. 
The distance between the bands increases as the distance 
AB diminishes. This is shown by simply varying the distance 
AB. 
2. Other things being the same, the distance between the 
bands is greater the greater the wave-length of the light em- 
loyed. is may be shown by having another pair of pieces 
representing a Across wave-length. We may also infer the 
effect of using white light. 
A C z 
Vay 
Uy 
Uj 
beat] 
The bright points are so situated that the difference of 
their distances from the two centers of disturbance is a multiple 
of the wave-length ; while for the dark points these differences 
are multiples of half the wave. — Other points might be 
mentioned but these are sufficien 
No attempt has here been mae to describe methods of get- 
ting the bands themselves by using light, because the necessary 
directions may be found in a number of books. Nor have I 
inted out the limitations and- inaccuracies in the method of 
illustration. These will readily occur to any one using it. 
far as this piece of apparatus is concerned what I have assumed 
to represent a bright line might be taken for the dark one by 
making only a slight change in the pieces of boar 
Lexington, Va. 
