172 TECHNICAL SURVEY 
and if placed high enough it not only can reflect to 
enormous distances but also becomes extremely 
effective. It was decided not to give this effect too 
much concern as all these calculations are made on 
the basis of horizontal stratification. Doubtless all 
sorts of small departures from a smooth curve occur 
at various rather large heights, but they do not occur 
perfectly stratified over areas of hundreds of square 
miles, and only such perfectly stratified departures 
could: cause embarrassing results. Accordingly it was 
decided that such fluctuations as occur probably 
cause fading or fluctuation but do not cause the 
particularly troublesome effect mentioned, because 
they are local and not stratified over large areas. 
