252 THE BOTTOM OF THE SEA. 



darkness increases with the depth, soon becoming 

 such that the workman has to grope his way about — 

 more especially where the bottom is muddy, and in 

 parts where it is impossible to see beyond a depth of 

 twelve or fifteen feet. To remedy this serious incon- 

 venience, attempts have been made to use an oil or 

 spirit-lamp, and even a simple lantern lighted with a 

 candle. A pipe, communicating with a pump, is 

 needed to convey the air necessary for combustion ; 

 another, rising to the surface, permits the escape of 

 the products of combustion. Without referring to 

 the inconvenience which was generally I'elt in working 

 these lamps and their two pipes, the light was always 

 found insufficient. The dense air transmitted by 

 the pumps gave rise to the singular phenomena to 

 be observed in compressed air-tubes ; the wicks car- 

 bonised, the light was pale, and lasted hardly a 

 quarter of an hour. These dijfficulties have been 

 overcome by employing the electric light. A per- 

 fectly watertight lamp of iron or brass encloses the 

 regulator of an electric light on Serrin's system. The 

 wires which conduct the current enter the lamp by 

 traversing a non-conducting plug of tow. The current 

 is derived from a pile of fifty elements, and a dazzling 

 light, equivalent to two thousand of Carcel's jets, is 

 obtained. The sides of the lamp resist the pressure 

 exerted by the water, an'l the gases, becoming dilatfjd 



