Short Electromagnetic Waves by a Crystal. a) 
give spots on the photographic plate which are in fact not there, 
and there is no obvious difference between the numbers h, h, h, 
which correspond to actual spots, and those which are not repre- 
sented. 
To explain this Laue assumes that only a few definite wave- 
lengths are present in the incident radiation, and that equations 
(1) are merely approximately satisfied. 
Considering equations (1) it is clear that when h, h, h; are fixed 
r E ae 
qn only have one value. However if h, h, h; are multiplied by 
an integral factor p, equations (1) can still be satisfied, but now 
by a wave-length ae By adjusting the numbers h, h, h; in this 
way, Laue accounts for all the spots considered by means of five 
different wave-lengths in the incident radiation. They are 
r= 03774 
X= 056840 
rv = ‘06634 
N— otc, 
r= ‘1484. 
For instance, in the example given above, where it was found 
that 
a: Voy: bed: 1 
these numbers are multiplied by 2, becoming 2.10.2. Then 
they can be assigned to a wave-length 
037 
a 
approximately equal to the first of those given above. 
However, this explanation seems unsatisfactory. Several sets 
of numbers h, h, h, can be found giving values of * approximating 
very closely to the five values above and yet no spot in the figure 
corresponds to these numbers. I think it is possible to explain 
the formation of the interference pattern without assuming that 
the incident radiation consists of merely a small number of wave- 
lengths. The explanation which I propose, on the contrary, assumes 
the existence of a continuous spectrum over a wide range in the 
incident radiation, and the action of the crystal as a diffraction 
grating will be considered from a different point of view which 
leads to some simplification. 
