[33] 



U. S FISH COMMISSION STEAMER ALBATROSS. 



35 



The wires are run through the tubes of these brackets, but in the 

 jointsof the swinging brackets thecurrent is transmitted through 

 insulated hinges, to which the wires are fixed by binding screws, 

 as shown at a in Fig. S, by which arrangement the wires are not 

 twisted in swinging the bracket. The wires are brought to the 

 binding posts in the lamp-socket, Fig. 9, between their binding 

 screws and brass conductors; one of these brass conductors is 

 soldered to the thin spun brass socket into which the lamp is 

 screwed while the other is connected, through the key, to a brass 

 disk placed centrally in the bottom of the socket, against which 

 one pole of the lamp presses when screwed in place. The key 

 is mounted on a, screw-thread of such pitch that one-fourth of 



a revolution will give it sufficient axial 

 motion to open or close the circuit. 

 The small number of parts used iu 

 these fixtures, their correct propor- 

 tions, the adaptation of their forms to 

 machine tool manufacture, and their 

 Fig. 6. beauty of design excite the admiration 



of both artists and mechanics. 



THE LAMPS. 



The lamps are of thin glass, pear-shaped, containing a thread 

 of bamboo carbon about as thick as a horse-hair. The small end 

 of the lamp (Fig. 10) contains glass of sufficient thickness to 

 make a tight joint on the platinum wire conductors which carry 

 the current to the carbon. The atmosphere is exhausted by Edi- 

 son's modification of the Sprengel pump, through a tube at the 

 lower end of the lamp, and the tube is then fused and broken 

 off. Platinum wire is used because its index of expansion is the 

 same as that of glass, thus preventing any breakage or leakage 

 from the heat. The bamboo-carbon, and platinum wire are 

 soldered together by electrically-deposited copper. One wire, 

 passing through the glass, is soldered to a small brass disk 

 which is centered on the top of the lamp (Fig. 10), while the other 

 wire is soldered to the spun-brass screw-thread which surrounds 

 the cylindrical part at the 

 top of the lamp, and when 

 the lamp is screwed into 

 the socket (Fig. 11) the 

 circuit is completed or 

 broken by the switch or 

 key already described. 



When the circuit is 

 closed the carbon thread FlG< 7- 



becomes heated to incandescence — from its high resistance — and 

 continues to glow, in vacuum, without burning, so long as the cur- 



