706 



SCIENCE. 



[Vol. II., No. 43. 



lamp of 750-canclle power, which we are now 

 using; and we find, in practice, that a no. 18 

 copper wire will carrj' the current without 

 heating. The power of this lamp, to be com- 

 parable with other arc-lamps, should be mul- 

 tiplied by four, as the commercial candle- 

 power of the arc-lamp is the aggregate of four 

 measurements, the photometers being placed 

 equidistant from each other in the same cir- 

 cumference. The power required to drive 

 these arc-lamps, though more than necessary 

 for others of equal p)ower, is j'et quite small. 



Efficiency of the arc-lamps. 



Indicated horse-power developed by the engine 



with two arc-lamps in circuit 6.69 



Horse-power required to drive the engine and 



dynamo 3.56 



Net horse-power applied to the shaft .... 3.13 

 Horse-power absorbed in the friction of the 



load 0.23 



Net horse-power applied to the revolution of 



the armature in the magnetic field .... 2.90 

 Net horse-power applied to the armature for 



one lamp {half of the last quantity) .... 1.45 



The number of eight-candle power incan- 

 descent lamps per indicated horse-power is 

 taken as a mean between the quantities as 

 determined above, i.e., — 



nb + 27.02 -f- 24.63 



25.55 ; 



and this quantitj' multiplied into the net horse- 

 power required to drive one arc-lamp gives 

 (25.55 X 1.45 =) 37.04, which is the power 

 in units, of incandescent lamps, to run one 

 arc-lamp of 750-caudle power. 



Fishermen iu nearly all parts of the world 

 use a light in their boats, when fishing at night, 

 to attract fishes into their nets ; and it is a com- 

 mon thing for flying-fish to come on board ship 

 at 'night if a light be advantageously' placed 

 to attract them. 



Until incandescent lamps were invented, there 

 were no convenient means of sustaining a light 

 beneath the surface of the waters ; and there is 

 consequently opened up to us an unexplored 

 field in fishing. 



Just what service our submarine lamps will 

 be, we are as yet unable to say : but, with the 

 small lamp which we use from one to ten feet 

 below the surface, amphipods in great num- 

 bers, silver-sides, young bluefish, young lobster, 

 squid, and flying-fish, have been induced into 

 the nets, and dolphins have approached it; 

 but whether the dolphins were attracted by the. 

 light, or were pursuing the squid. Professor 

 Benedict, the naturalist of the ship, was un- 

 able to say. Squid are especiall}' susceptible 



to the influence of light. I am informed by 

 the very emiuent authority of Professor Ver- 

 rill, of Yale college, that a heavy sea, breaking 

 upon a lee shore when the full moon is casting 

 its rays across the land into the sea, will throw 

 hundreds of squid upon the beach in a single 

 night, — an evidence of their moving in the 

 direction of the light until caught in the spray 

 and hurled upon the shore. 



To succeed in producing the light at consid- 

 erable depths has been bj' no means casj-. 



The Edison companj' first prepared a lan- 

 tern of two thicknesses of glass, hemispherical 

 in form, with its flat side tightly joined to a 

 bronze disk on which were placed three sixteen- 

 candle power B lamps in multiple arc. At a 

 moderate depth it burned beautifully ; Init at 

 about a hundred and flfty feet the packing 

 leaked, and the sea-water, entering, short-cir- 

 cuited, and the lamp was extinguished bj' the 

 destruction of the cut-out plug. A similar 

 lamp was then tried with improved packing; 

 but its glass walls were crushed by the press- 

 ure of the water, and it was extinguished. 



The next essaj' was with a single Edison 

 lamp, its glass vessel being cylindrical in form, 

 with hemispherical end, to give it strength ; 

 its thin platinum wires extending through one 

 end without &ny external attachment. To 

 these delicate wires I succeeded iu soldering 

 the copper wires of the cable, but broke (or 

 cut) off one of the platinum wires at the point 

 where it enters the glass, while putting on the 

 insulation. When it is remembered that a 

 hundred fathoms depth of water brings a press- 

 ure of over two hundred and fiftj- pounds per 

 square inch on the lamp, it will be understood 

 that great care was required in every proce- 

 dure. 



Our next attempt was with a single Edi- 

 son lamp exactly the same as the last. I suc- 

 ceeded iu soldering and insulating the joints 

 perfectly ; but the pressure of the water upon 

 the insulation cut the delicate platinum wire 

 on the glass before it had reached a hundred 

 feet in depth. 



The Edison company then produced a lamp 

 in which the platinum wires were soldered to 

 copper wires in a glass cavity, and filled in 

 with rosin, so that copper wires, about no. 30 

 in size, projected from the lamp for our attach- 

 ment. I coiled the copper wires spirally, and 

 soldered their ends to the ends of the heavy 

 wires of the cable, separating them by a small 

 block of pine wood : this gave some freedom 

 of motion, without danger of cutting or break- 

 ing the wires. A paper mould was placed round 

 the joint, and filled with warm ' gulloot. ' When 



