36 COAST DEFENCE AGAINST TORPEDO-BOAT ATTACK. 
The manoeuvres have very clearly demonstrated that the effective 
lighting of water areas is not so much a question of brilliancy of ray 
as of selection of site for the installation and that in siting lights near 
the sea level the Engineers are in error. 
PIG. IV. 
If E F is the curve of the earth and there is a light at A throwing 
a ray A A! A" there is a dark portion between E and A', which affords 
a shelter to boats: If now the installation be moved to B the range 
of the light is vastly increased and there is practically no dark space, 
except possibly close in shore, where generally no light is needed, or 
if it is can be supplied by a weak instalment flanking the shore, or by 
temporarily depressing B . 
The writer has never had an opportunity of using an 
electric lights ^ electric light installed at a greater height than of 
should work. about 80 feet, and that a weak portable one, but even 
at this height it appeared to be more effective for gun 
work than far more brilliant lights lower down. A high installation 
has not to drive its light through so many layers of dense atmosphere 
and smoke and it has a much larger target to light up. Trial might 
show that the higher a light is placed the better. 
But another fact was frequently recorded during manoeuvres where 
low sited lights were used which does not seem to have been noticed 
before and which is much in favour of torpedo-boats. 
PIG.V. 
The rays were seen to be deflected upwards increasing the dark area 
E A' A". Where one light was a few feet higher than the other, it 
was thought that this deflection was not as great in the case of the 
higher light as with the lower. This needs further experiment and 
confirmation. Some mountains, seven miles or so away and 2,000 
feet high had their tops brilliantly lit up by a very powerful low sited 
light, the greater part of their mass being in shadow, yet the light was 
being employed to show the surface of the water not 1,000 yards away 
from the light. 
