314 THE SCIENTIFIC PAPERS OF 



unless the weighted armature of the electro-magnet was in its 

 distant or unattracted position. The attraction taking place, the 

 circuit was broken at the point of a platinum pin, which was 

 drawn from a mercury bath, and a brilliant discharge of extra 

 current ensued. The current being thus broken, the armature fell 

 back and re-established the circuit, when it was again attracted, 

 and a discharge again took place, and so on during the periods of 

 time when the circuit was established on land. The mercury was 

 continually renewed at the point of contact by means of a 

 circulating pump, worked by the electro-magnet itself, which 

 latter had to be very powerful in order to produce an intense 

 light in its discharge. The point of discharge was placed in the 

 focus of a dioptric or catoptric reflector, upon the beacon or buoy, 

 to be lighted. This apparatus had only lately been completed, and 

 had not yet been tried at sea ; but it had been at work experi- 

 mentally for some time, and appeared to give very constant effects. 

 If this apparatus was constructed for throwing the light only 

 through a limited arc, the effect would be much intensified ; and 

 in that form he thought it might be placed with advantage at 

 narrow entrances, where each light would tell its tale by the periods 

 of successive flashes peculiar to itself ; and since the succession of 

 flashes could be varied at will by the contact arrangement on land, 

 the apparatus might also be used for conveying special warnings or 

 signals to vessels out at sea. This apparatus was only applicable 

 to a succession of flashing lights. 



