48a 
MINUTES OF PEOCEEDINGS OF 
centre. To the outer end of each arm a lamp is suspended on gimbals, 
the whole apparatus being accurately balanced. As the three lamps form 
a figure of the same shape as the vane for day signalling, and as the 
lights at the circumference are nearer to each other than to the third and 
central light, the position of the signal can always be ascertained; for one of 
the lights at the circumference may either mark a horizontal or vertical line 
in connection with the centre light. It has, however, been found that lights 
cannot be distinguished from each other unless they are at considerable dis¬ 
tances apart, according to the range at which they are to be visible. White 
lights are far superior to coloured lights, and three white lights, arranged 
as in Fig. 3, may be made to assume any of the forms indicated in 
Fig. 1, as also the three or four extra signals available for special use. When 
these extra signals are used at night, the two lights nearest each other (at 
the circumference), would assume the vertical or horizontal positions, and 
thus be easily distinguished from the ordinary clock-signals when these 
lights are never either in a horizontal or vertical line. 
October 7, 1871. 
