34 COAST DEFENCE AGAINST TORPEDO-BOAT ATTACK. 
Uncertainty 
caused by 
fixed beam a 
possible ad¬ 
vantage. 
the fixed beam severely alone. Nothing would be so disconcerting to 
a boat commander as to find the fixed beam, under whose shelter he 
is comfortably waiting his chance, suddenly move on to him. He 
would have to go. 
Harrow There may be, and probably are, localities, such as 
channels. comparatively narrow channels across which an electric 
beam has complete power, where it may be thought 
distinctly advisable to keep a beam, capable of wandering, as a 
general rule steady on one bearing; but the power of motion and its 
judicious use is most valuable for gun defence. Boats will never 
effect much singly; moving beams are scarce, and there are no 
fighting lights, and thus the wandering beam is often occupied with a 
boat sent in purposely to show itself while the true attackers are 
dodging the rigidly fixed beam. 
The one good thing with which a fixed beam may be 
credited, when conditions are favorable to its use, is 
the uncertainty it imposes on the attack. The care¬ 
fully laid schemes of attacking boats are a good deal 
upset if they depend on a time basis. It is impossible 
to say when the light will break down, and if ordered 
to rendezvous at a certain hour inside the fixed beam for the purpose 
of a combined rush at a given hour it is probable that only one or 
two boats will have succeeded in reaching the rendezvous and some 
confusion may result. It is impossible to foresee everything and in 
such a case there is likely to be either hesitation or premature action, 
either of which may lead to failure. 
If there are no good lookout-men the use of a fixed 
beam in a narrow channel may be an advantage. A 
lookout man must be bad indeed if he does not 
detect a torpedo-boat crossing a light at close range ; 
but a torpedo-boat is very poorly handled if she runs 
into a fixed beam, except to draw attention off her consorts. She can 
always get through if she waits long enough. 
A concentrated beam penetrates a much greater 
distance in nearly all states of the atmosphere than a 
dispersed beam, but it covers a comparatively small 
area of water. The dispersed beam gives a dim 
diffused light that often does not show up torpedo-boats as a good 
target for guns unless the boats are fairly close in, while it is 
noticeable that guns rarely open fire so rapidly when a boat is first 
discovered in a dispersed beam as they do when a concentrated ray 
catches the craft. There seems more hesitation in deciding what is 
seen. Both with concentrated and dispersed beams the water just 
outside them appears extra dark, forming the 6 dark ray ’ before 
Fixed beams 
useful where 
there are no 
trained look- 
out-men. 
Concentrated 
and dispersed 
beams. 
No matter what the state of the atmosphere or the 
of the sea, boats are absolutely invisible in these dark 
mentioned, 
appearance 
patches. 
The effect of site on the efficiency of electric lights in showing 
guns their prey does not appear to have received any consideration at 
